I'd go on the deal sites and see what they have for ideas! Couple places we've enjoyed a lot without kids/prior to kids:
Niagara Falls/Toronto/Fingerlakes area in NY
Washington DC
NYC
Hawaii (probably above your budget)
San Diego
Cape Cod, MA
New Orleans
Niagara Falls/Toronto/Fingerlakes area in NY
Washington DC
NYC
Hawaii (probably above your budget)
San Diego
Cape Cod, MA
New Orleans
But Niagara Falls, Upstate NY, NYC, Boston/Cape Cod, Washington DC are high up on my list too!