I wouldn't say that people are SELLING them due to cost of ownership. I think people are selling them for a while myriad of reasons probably the same reason they sell any car (bored of it, grow out of cars, want something newer and more competitive etc...). But I do think it hurts DEMAND, since a lot of people who could potentially afford to be buying one of these cars and desire to buy one get scared away when they see headlights going for 10k a pair, hoods going for $7k, new windshields unavailable etc... Especially younger guys who want a car to drive, not a a collector's piece.
To be fair, modding these cars has always been expensive as well which might further turn away those who would want something older and unique like a Viper but also wants to remain competitive with newer stuff. It's a unique platform in that I see very few new owners modding them anymore. People buy them to keep them stock or stock-ish and just cruise them knowing full well they'll get their doors blown off by a new Coyote 5.0, bolt ons Scat Pack, Hellcat, bolt ons B58 BMW etc... That further limits the audience. You'll look at a car like the MK4 Supra and GNX, I've always believed much of the reason they became so iconic was because of how easy and affordable it was to keep up with or beat newer stuff for so long with those platforms for so many years after they were out of production. It kept them relevant for longer and cemented their legacy. Even looking at old muscle cars, there's obviously a high demand for a factory stock 70 challenger but being part of that community you can see how commonplace gen 3 hemi swaps have become in addition to all the guys building big block and small block strokers etc.... Point being a huge portion of the community purchased one with the intent of 'keeping up with the Jonses' in terms of performance, not just driving it around in all original/near original form. You see very few gen1/2 vipers being modded these days. I don't really know if that's because people think that originality is going to increase their value or if it's because of the cost of modifications though, maybe a mix of both. It's a tricky spot with the older V10's. It's a great engine, but it can get very costly very quickly to modify. Since it IS a v10, swapping it out for a much cheaper to mod late model v8 like you see tons of guys doing in most older GM or Mopar platforms with LS or Gen 3 hemi swaps sort of kills the car's identity since having a massive V10 was so much of what made a Viper a Viper.