So I had my oil changed at the dealer today at 90,000, and they told me that my engine mount has collapsed on the right side and is weak on the left. They want $785 to fix it. So I'm assuming I should do this, correct? Will the car not work if the other one goes out too?

I am past any warranty, even though they know this is a problem and there is a TSB for it. Of course, I seem to be able to get the parts for $200 here (http://search.store.yahoo.net/cgi-bin/nsearch?catalog=yhst-24809172479195&query=rx-8%20motor%20mount&searchsubmit=Go&vwcatalog=yhst-24809172479195&.autodone=http://www.mazdaparts.org/mazda-rx8-motor-mount.html), and the TSB says its 1 hour of labor. Somehow I feel I'm getting ripped off.

Any thoughts or suggestions?

I felt the same way when I had mine replaced. However, you do need to get the engine mounts replaced one way or another, they are very important IMO.

you are getting ripped off. Call Mazmart get some used mounts for $150 or so and put them on yourself. it is not hard to do--just a little work.
These are hydrolic motor mounts ---unless the fluid has leaked out then they have not collapsed. They still may need replacing but it is not an emergency.
od