I think they pretty much had to do this if they were going to add item trading. Otherwise people would be selling items on ebay and neither Valve nor the community contributors would see any money from it, not to mention the increased customer service cases where people got scammed.
The prices are reasonable, you get them permanently (unlike a lot of other microtransaction games), and if you don't want to spend any money, everything that effects gameplay can be obtained quite easily through gameplay just as before. Also, they aren't going to stop releasing items, game modes, updates, etc. for free, they just give people another couple of ways to get them (buy or trade). Personally, I don't have a problem with it.