I think that AE with it's many options for color grading plugins would be possibly your best option on a PC for you budget. Rendering isn't all that slow, but the fact that AE wasn't really built (in my experience) for RT playback sucks when grading, or doing anything really.
I have tryied Colorista and I'm not that impressed. Yeah, I know many people find it cool and usefull but I need a real power, not just improved 3-Way CC from FinalCut. I've seen really nice effects created with Nuke and I'm looking at it now. Color Finesse seems pretty interesting as well. How does it comapre to Color?