Touch screens are around $50usd and resell for $100-250 depending on device. Back glass on iPhones are about $15 to replace. Biggest downside to fixing them yourself is that it voids the warranty, although if you're going to fix something like that on your own you'd probably never use the warranty anyway.
Mine is broken So is the iPod button I'm gonna buy the kit that comes with the screen and button. Then gonna have my sister do it since she fixed hers. my warranty is up.
If you're fixing a broken home button, make sure you get the entire internal assembly and not just the visible button itself.