how hard is this to replace?
 

im thinkin of buying an 86 n/a but it needs new rear wheel bearing, and gear shifter bushing, is that bad?

Replacement of the shifter bushings does not appear to be very difficult or expensive. Replacing mine on my '87 RX7 is on my to do list and I plan to use this guide:
http://www.mazdatrix.com/faq/shiftbsh.htm

Shifter bushing = Easy
Rear wheel bearing is harder. If you don't have access to a bearing grabber and a bearing press then you may have to get it done for you.

I need to do the same thing to a 87 i like tha link....