20 dollars on a PSU? You dont want to cheap out on the power supply. I'm no pro but i dont think you are ever really going to build a future proof pc for 3300 bucks. What would i do ask around on build a pc both here and on reddit and see just how large of a power supply you need and get the best small power supply you can afford if you buy a cheap psu it could literally fry everything and at the very least give you terrible performance. I would try to bump everything you can down a bit. For instance the HDD why not go with a smaller one and then pick one up later so you can increase the storage. Bump it down to 4gb of ram.
Threw this together real quick on pcpartpicker. I wouldnt use all these parts at least not without researching them first. Im not saying they are bad just look around a bit and research all your parts look at reviews on amazon and newegg lets you see if parts have a common fault in them or something like that.
PCPartPicker part list: http://pcpartpicker.com/p/z7E2 Price breakdown by merchant: http://pcpartpicker.com/p/z7E2/by_merchant/ Benchmarks: http://pcpartpicker.com/p/z7E2/benchmarks/
I was planning use crossfire it with a HD 6670, and I heard the ram wouldn't make a difference if I did. I hope... Anyways it was just $26, and I was planning to upgrade anyways later on