Senate Democrats discovered over the past few weeks that there can be a hefty price to pay for bipartisanship after a trio of Senate Republicans compelled them to shave more than $100 billion off the economic stimulus bill.

With the U.S. economy in a downward spiral, the price a handful of Senate Republicans could demand for their votes on future economic recovery plans may become more and more painful for both President Barack Obama and Congressional Democrats.

After all, only three Republicans out of a total of 219 in both chambers voted for the $787 billion economic stimulus package passed last week. And members of both parties predicted the sticker shock that will come from Obama’s emerging plan to shore up the financial sector — along with another potential stimulus measure, regular appropriations bills and supplemental war spending — could harden GOP hearts, as well as those of some centrist Democrats.

“This is a town where you’ve got to count votes, and for those [Democrats] who are not happy and think that too much was extracted, they need to count votes,” said Sen. Ben Nelson (D-Neb.), who helped broker the Senate deal that ensured three GOP Senators would vote for the stimulus measure.

Senate Majority Leader Harry Reid (D-Nev.) will likely need 60 votes for every major economic recovery bill that comes to the floor, given any one Senator can object on procedural grounds and force a supermajority vote on legislation.

Though Speaker Nancy Pelosi (D-Calif.) lost seven Democrats and still passed the stimulus by a comfortable 246-183 margin, Reid was reliant on the votes of Sens. Susan Collins (R-Maine), Arlen Specter (R-Pa.) and Olympia Snowe (R-Maine) to get it passed.

For that, he had to trim $108 billion from the Senate bill and tens of billions more in conference with the House.

Collins — and Nelson — said that while they are comfortable being in the spotlight and negotiating bipartisan deals, they cannot be counted on in every instance.

“I am not an automatic for either side,” Collins said on Friday. “Neither am I,” chimed in Nelson, who was standing next to her at the time.

Specter said he is not necessarily comfortable continuing to provide Democrats with their 60th vote from here on out.

“I’d feel less uncomfortable being the 61st and even better about being the 67th,” Specter said. Still, he said he would evaluate each issue on a case-by-case basis.

Currently, Reid is operating with an otherwise comfortable 58-Member Democratic caucus, but the stimulus debate showed just how difficult getting to 60 can be, regardless of the size of the majority.

Reid’s difficulty could be compounded by the continued absence of Sen. Edward Kennedy (D-Mass.), who is battling a brain tumor. Kennedy’s absence could be counterbalanced by comedian Al Franken, if he is declared the winner over former GOP Sen. Norm Coleman (Minn.). The contested 2008 race continues to wend its way through state courts.

Regardless, Reid found that getting Republican votes wasn’t his only problem on the stimulus. More than a dozen centrist Democrats were involved in the Nelson-Collins negotiating sessions.

“I think it becomes as increasingly difficult to get three Republicans as it does to hold all the Democrats,” Sen. Richard Burr (R-N.C.) said.

And Burr said Republicans aren’t necessarily trying to have a partisan throwdown over the economy.

“When we [criticize] the size of this, this is not just about egregious spending. This is about an obligation to the future,” Burr said. “How do you fund everything else?”

As Obama’s one-time presidential rival, Sen. John McCain (R-Ariz.), pointed out on the Senate floor Friday, “these numbers are staggering.”

The current national debt stands at $10.7 trillion. The federal deficit is at $1.2 trillion. With the stimulus last week and a financial industry bailout last fall, Congress has already spent $1.5 trillion to rescue the economy, and the Treasury Department has been floating another Wall Street aid package that could cost an additional $1.5 trillion in public and private funds.

Plus, the fiscal 2010 appropriations bills will likely come in at or around $1 trillion.

The more than $400 billion omnibus that the House may take up next week and an expected $80 billion Iraq and Afghanistan war supplemental seem like trifles in comparison.

Part of the problem is that both parties — but particularly Republicans — are gun-shy after getting pummeled during the 2008 elections for their support of the Bush administration’s $700 billion Wall Street bailout plan, which both sides said was mismanaged and weak.

Sen. Lindsey Graham (R-S.C.), who supported the bailout, said the GOP skittishness after the financial industry rescue, coupled with Democrats’ push to spend lavishly in the stimulus on questionable programs, could hamper bipartisanship going forward.

“What we’ve done is we’ve made it more difficult to solve the fundamental problem of the economy by having a stimulus package passed in such a partisan way that soured the public,” Graham said. “So a new request to fix housing and banking … it’s going to be a steeper hill to climb.”

He added that for many Members, politically, “It’s just easier to say ‘no.’”

Still, Graham and other Republicans indicated there is hope for Democrats, particularly when it comes to another financial industry bailout plan.

“Here’s my advice to Republicans who felt shut out and disappointed [by the stimulus]: ‘We still have to fix housing and banking,’” Graham said. He added, “My message to the administration is count me in for finding a solution to housing and banking, because we have to.”

A surprising GOP ally for the administration could be Sen. Judd Gregg (N.H.), who removed himself from consideration to be Obama’s Commerce secretary last week.

Though he said his policy disagreements with the president led him to withdraw his nomination, Gregg explicitly noted that he would be in Obama’s corner on many economic issues.

“I do believe genuinely that I can be even more effective for this presidency in the Senate than, maybe, even in his Cabinet. I still think I have a fair amount of influence in getting things done around here,” Gregg said.

He added, “And there are going to be a lot of issues on which I’m going to want to jump in on and carry his water here in the Senate, and hopefully be successful.”

But Senate GOP votes, like those of Collins, Specter and Snowe, will undoubtedly come with a price tag, and the pressure from other Republicans to unify against Democratic solutions to the economy may only get more intense as time wears on.

Sen. Pat Roberts (R-Kan.) said he hopes the three GOP moderates will actually deny Democrats their votes in the future, saying the stimulus measure was more a wish list of Democratic policy priorities than an economic recovery bill.

“I would hope that the three amigos — if you wouldn’t endanger your life if you got between them and a TV camera — that maybe they can come back in,” Roberts said.

Democrats are wary of just that problem, which was clear Friday on the Senate floor when Sen. Charles Schumer (D-N.Y.) pleaded with Republicans to come to the negotiating table.

“To my colleagues, please, on the next bill — it is too late for this one — rethink the attitude,” Schumer said. “We are trying. … Republican input, albeit from three, has been large in this package. Join us. We want you to.”