Prices are rising for sure, but that doesn't put me off per se, the thing that does is trying to be part of the community and selling stuff at prices that help people fuel their hobby, only to find them up for sale elsewhere very quickly for way way more. This gets my goat as it puts me off selling on here for what I feel are mates rates (I have only met a few retro bikers in person, but we are all virtual mates with a shared passion), but some abuse that. I try to answer wanted ads now rather than sell as at least then I know (kind of) that someone needs something for a build rather than someone scooping up the generosity to line their own pockets.
As someone has mentioned, we all get a bargain from time to time, and selling bits helps with the next build, but it's done with the hobby not profit in mind, and the bargains are passed on as such.
As for modern parts prices, I've ventured into 29er and 27.5er builds and kitted them out with top end gear but paid a fraction of the price for the parts (mainly xtr or xt). Quality is way lower than the retro equivalents, take xtr 11 or 12 speed for example. A new cassette today will set you back almost as much as I paid for a full giant bike kitted out in full dx back in the day. Madness.