to answer your questions:
how much? They go for about 100 bucks on rx7club, so... let's say 60 + shipping.
Condition? My friend gave it to me when he converted his GTUs to a manual steering rack (for weight and racing), and he said it worked just fine.
How hard is it to put in? I've no idea, since I'm not going to be using it. I got it because I was originally going to do an LT1, and wanted the ease of power steering. Now I don't need it, since I have no weight over the front wheels. Much like the rest of the stuff on this board, it's a one-off swap dealie.
On the upside, if someone wants to make the swap, lot of guys on rotary boards ditch PS for manual racks.