I am collecting 1:500 models and yes, prices have gone up quite a bit over the last couple of years. It doesn't help that there aren't many manufacturers anymore. It's pretty much German Herpa and that's it.

Some of the models you are looking for won't be easy to find in the 1:500 scale, you will probably have much better luck in 1:400 which is more common here in the US. You won't be finding much in your price range though unless you look for used models on eBay.