Also evaluate whether you can throw money on an exchange and make more money than if you bought the hardware. You can't ignore the fact that this setup you are proposing will give you about about 2 GHash/s (give or take) and cost you about 1.1 to 1.3 kWh of electricity. At $0.15 per kWh, that works out to just over $4 per day to generate bitcoins. Network difficulty and value fluctuate (difficulty going up and value going down). You have to take these factors into consideration if you choose to sink some money into hardware.
Also remeber that you have cooling costs involved. Winter is coming in my part of the world, but if you live elsewhere, keeping your expensive hardware cool is pretty key to extract long term profits. Cards get to hot, and you have a lot of wasted money sitting under your desk.