I plan on crossfiring 2 Radeon 6950s since I have one in my current computer, so I know I'm going to need a sizable PSU. Once I get the money I also plan on getting a good cooler to overclock the 3570k (I could also use some help on this, but that's for a different post). How many watts would I need in my PSU and what should I go with? If possible, keep the price in 80 dollar range, but I can go to 100 dollars if needed.
For a system using two Sapphire Radeon HD 6950 [100312-3L] graphics cards in 2-way CrossFireX mode AMD specifies a minimum of an 700 Watt or greater power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 50 Amps or greater and have at least four 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most critical factor.
Overclocking of the CPU and/or GPU(s) will require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock you are trying to achieve.
The Corsair Builder Series CX750 ( SKU# 75-001447 / CP-9020015 ), with its maximum combined +12 Volt continuous current rating of 62 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with two Sapphire Radeon HD 6950 [100312-3L] graphics cards in 2-way CrossFireX mode.
CORSAIR CX Series CX750 750W for $89.99 ($69.99 after $20.00 rebate card if purchased between January 22, 2013 and January 28, 2013 from Newegg.com or Newegg.ca)