Well I have just the thing for you….
Pixelmator is down to £10.49 for a limited time at the Mac App Store. An absolute steal…
Pixelmator offers much of functionality of Photoshop for a fraction of the price. It is small and nimble and makes the most of many core OS X technologies such as Open CL and Grand central to really make it fly.
Check it out here www.pixelmator.com
I have no affiliation with the team, I am just recommending it as is is an absolute steal at 10 times this price.