Have you thought about any particular year that you want. Do you want bone stock, or some modifications? What about mileage? It's a tough decision, I too am looking for a Viper to buy, and I want to keep my price under $40K....since I do not want to have to sell my other "toys".
I have found that 1994 and 1995 are more likely to be in the $30K to $35K range in asking price (but I have not actually gotten into negotiations yet). Also, some 1996's are just at the $40K (or a little under) but they typically have mileage in the 30,000 range at that price.
Check autotrader, but I have an the pickin's are slim there. The classifieds here have more selection, but the asking prices are higher...these guys know what they have and won't give it away!
Good luck, I am hoping to be in a Viper by the end of 1st Quarter 2002.
Anyone want to buy a 1989 Jaguar XJ-S Convertible