Outside groups have spent more than a half-million dollars on the special election in New York’s upstate 23rd district with just under a month to go in the race. Former Rep. John McHugh (R) vacated the seat to become secretary of the Army, triggering the hotly contested Nov. 3 election.

The biggest spender thus far has been the Club for Growth’s political action committee, which has spent $275,000 on television and radio ads on behalf of accountant Doug Hoffman, who is running on the Conservative Party line.

The club’s ads don’t mention Hoffman, however, instead going after the two major party candidates — Republican Dede Scozzafava and Democrat Bill Owens — for being too liberal. The club’s spending could be a game-changer if it succeeds in raising Hoffman’s profile enough to make him an effective spoiler.

The National Republican Congressional Committee has doled out $247,000 in independent expenditures in the race, primarily for ads criticizing Owens and touting Scozzafava, who led in the first independent poll released by Siena College last week. The race, however, remains “wide open,— in the words of pollster Steven Greenberg, and Scozzafava will spend the next month fending off attacks from the right as well as the left, with conservatives objecting to her centrist record as a member of the state Assembly.

The Democratic Congressional Campaign Committee rounds out the spending bonanza with $130,000 worth of media buys praising Owens, an attorney and first-time candidate, and attacking Scozzafava’s record.