I just recently purchased a used factory hardtop for my '98 RT. I searched around to find a red one, but most of the time found black or gray. Prices ranged from $1,200 - $2,400 plus shipping (which for me was anywhere from $100 to $250). There was just a used factory Gen II top in red on Ebay a few months back, asking around $1,500-$1,600.
I was fortunate, as I think patience helps. I picked up a red hardtop from a '98 RT from one of the members here. He was great, we agreed on a price of $1,400 including shipping and then he gave me $50 off once we were finalizing the deal. Built a shipping crate to ship UPS. Try to be patient and buy from a member, I'm now convinced that is the first place to look.
Other places to try:
- Jon at Parts Rack, he usually has a few used sitting around
- Call some of the Viper performance shops
- Obviously, Ebay, but that is a really hit or miss thing
BTW, you didn't say what generation Viper you have. If you are looking for a Gen I top, then the member I bought mine from may still have a Gen I top in excellent condition.
Good luck on your search.