For that budget, I have to agree with above.
I doubt the bidding will end at $550. A good way to check, is to use an advanced eBay search, and search for completed listing. Remember an unsold item means nothing, look at how much stuff actually SOLD for.
A current generation 13" i5 MacBook pro could handle CS6, the HD4000 graphics are leaps and bounds ahead of anything previous. Though of course, a 15" model with a quad core and integrated graphics would be better! Naturally. However I use a 13" MBP with SSD's and upgraded RAM for CS6 quite a bit. I prefer the form factor and have a home built PC (quad core, Radeon HD5870) that I use if I need the performance. However, that requires a significant increase in your budget!
$500 could get you a decent, baseline used Windows laptop with incrementally more performance. Unfortunately, the only Mac notebook you're going to find in that price range is one of the older (before the most current generation, and even that's been discontinued a while) white polycarbonate MacBook's, which won't give you the performance you need.