Bought iMac from a reputable store online that does not charge shipping; problem is that they only offered the i5 3.1ghz and I needed both turbo boost as well as hyper threading for music and video applications. Decided to buy 3.4 i7 and install myself along with an OCZ Vertex 4 to have the fastest iMac possible.
With this kit and the repair manual (as well as an extensive history of tearing down and fixing things...mostly out of curiosity) I was able to install the SSD and CPU in approx. 45min without a hitch.
Make sure that you have confidence and patience when repairing anything. Do not get frustrated and practice on old, broken items before going forward with any good, working items.