Be prepared to loose a couple of hours of your life but it’s quite doable. Screen is quick and easy, rear housing means stripping phone completely down.
A local pone shop to me offered to do it for £50, I got a new housing off t’internet for £15… if I had to do it again I’d probably just pay the £50. If you do decide to do it your self get a good set of precision screwdrivers and don’t use the chocolate ones that come free with the case.
iFixit for the guide and Maplin/Ebuyer for the screwdrivers. Screen is easy-ish (I did the one on my 5 twice, clumsy, moi?) if you can get the bits with the buttons in place then it will save you quite a bit of time and faffing.