Personally, I'd let them sit on the offer for awhile. The longer the vehicle sits on the lot the more they're willing to deal. Maintain contact with the sales person to let them know you're still interested and if they come down in price, that you'll consider it.

In the meantime, go shopping!! Go check out other dealers. Don't rule out buying new. You'd be surprised what you could get. This way, with whatever car you finally end up with, you know you got the best deal possible. Also, I strongly believe, that the discounts dealerships give you is partially dependant on the area you live in (and the competition).

Good luck!
-Moto