I have bought many phones, and spare parts for phones, off Ebay. As long as you know what it is you want you can buy them pretty cheap - here at least.
I use a Motorola Defy (needed a robust phone) which retails at about £160, but you can get then reconditioned off Ebay for about £50.
In the past though when I have killed a phone and can't identify which part is faulty, I usually try and get a "spares or repair" phone off Ebay and use it as a donor to repair the other one. It is surprisingly simple to fix them and some phones can be bought for £15 because they have a cracked screen (good news when it's the motherboard I need).