OP, I do this on the side, for a decent amount of extra change. I live in a city of 150,000 less than an hour North of San Francisco, so there is A TON of competition.
It'll cost you a few grand in parts, which is: Low-end CPUs for EVERY socket from the last five years, a pair of FB-DIMMs, a pair of DDR2, 3x1GB of DDR3, DDR2/3 So-DIMMS and maybe even a 512MB stick of DDR. You'll need a PCIe video card, a PCI video card, believe it or not an AGP card (ALL must have VGA+digital), and both PCI and PCIe SATA+IDE combo controllers. Add a solid 20+4 PSU, PCI/PCIe NICS, and a monitor which has both VGA and DVI inputs. Think of EVERYTHING you could build a system with.
For LGA1156 you'd want: Pentium G6950, 2x1GB DDR3 1333
FORLGA1366 you'd want: Both a P4 and a 45nm Core-2, and 2x1 DDR2
You get the idea.
For charge, I charge $50/Hr, with a 3-hour minimum, which is about average, and I don't do phone tech-support on top of that. I charge the 3-hour minimum for a consultation. If you give free phone support, I hope you live in a land where there's no idiots.
Good Luck!
Daimon
EDIT: OP, I almost forgot: You should think of this as a way to make you extra cash, and not because you help your friends and you like computers. I've lived for computers since my Commodore PET, and I help friends for free, but once you encounter the incredible variety of idiots out there, I hope you'll see them as what they are... stuffed wallets.