I would think it cost maybe 200 per wheel? I would take that 800 save up another 400 sell the wheels you have and then buy a really nice set, that's just me.
I've driven one on the old moroso course and the only thing I have to say is the car handles amazing, but the lack of TQ is really really bad. If your starting g out I'd get a z over a rx8 , and that's coming from a Mazda lover.