I'd highly recommend just searching on Craigslist for some used Mustang wheels. I got my 2010 19" Track Pack wheels in mint condition on Craigslist for only $480. Yes that's for ALL FOUR. If you do your research you can get a really nice deal on some good used ones. Just don't rush it. I spent at least a few weeks looking for mine.
Also, I found mine on the Buffalo site so make sure to go to other Craigslist sites for nearby cities. There's also the Classifieds area here on NYM.
Also, in case you didn't know, TireRack and DiscountTireDirect have an area on both of their sites where you can see what certain wheels will look like on your car. That helps quite a bit in finding something that looks good.