So I bought a pre-built and have been slowly upgrading it piece by piece myself, so I can learn how to put everything together. Anything I need help with, I'll google guides or ask my computer-savvy friend. I'll be building my next PC myself, hopefully.
My current PC (purchased 1 year ago, upgraded over time):
-ASUS M4A78 Plus MoBo
-550W PSU (ePower? Whatever brand that is lol, but it hasn't shown signs of being inadequate so whatever).
-AMD Phenom II x4 970 BE @ 3.5GHz
-4GB Kingston HyperX DDR2 RAM @ 800MHz
-ATI Radeon 4870 1GB
-500GB internal HDD; 250GB external HDD; 160GB internal HDD for FRAPS.
Performance: It runs Mafia II in 1080p, Max settings, AA Off, AF x16, V-Sync On, PhysX off: @ 46 avg, ~21 min FPS in benchmark, but feels like 50-60FPS when I actually play it.
Price: $550 (pre-built). Upgrades: $290. You can build better PCs for $840 I imagine, but I'm new at this

I did not include my monitor, external HDD or OS in the price, b/c they carried over from my last PC.
Once I learn how to and then actually do build my own computer myself, I'll start learning how to overclock.