HD6450, HD6570 and HD6670 are the three cards that you can use to CrossFire your APU's integrated graphics with, so that you can use both in games, however the HD7770 will be stronger than that crossfire setup, and it's a relatively cheap GPU now.
As for a power supply unit, you could look at the Corsair CX430; it's a relatively cheap and good power supply. I know many people will advise you not to go for a CX, but with the budget, you won't be able to tax it anyway.
As you stated your budget is 200 dollars; the PSU will be eating $40 and if you can get a NVIDIA card, then the 750Ti is great at $140. It doesn't require a supplimentary power connector; it's quiet and power efficient.
Another route you could take is sacrifice a little on the graphics card now and go for a good power supply around $100, such that you'll be able to upgrade to a GTX 760 or so in the coming months, or if you want to go AMD, you could even get a R9 270x or 280.