Your best bet is to start a thread following the sticky at the top of the new build forum with budget and other info and we would be able to help you stay in budget with all your components.
To me the $20 is worth it, but I don't know your whole budget.
Have read it before, thing is, i wouldn't want to overclock i dont think, but for an extra £20 it would be nice to have the option...
Also awhile i kinda know what i am doing its nice to have it cleared or be put straight by guys that have done this before, so is what im doing is writing out a list with CASE: 3 different ones, GPU: 3 different ones, and so on then make a thread to see what everyone thinks out of them.
EDIT: my budget for the system is £700, but im using my 60" TV and 5.1 Surround sound.