I think I'm going to have to replace the throw out bearing on my 2000 5spd..
What are the consequences if you don't replace it? Can I wait til its time to change the clutch? How much does this usually cost to get it done at a shop?

 

Labor is the same as changing the clutch. Do not put this off, unless you want to get stranded when the TO bearing finally stops working completely.
A local maxima shop around here charges $250, but a lot of places charge about $400-600+.

 

if you replace the TOB you really should do the whole clutch too.

 

Probably $300-$600 labor. Since you're paying all that labor you may as well get the clutch replaced as Jsutter said. That'll be about another $200 in parts. MAKE ABSOLUTELY CERTAIN THAT YOU DON'T BUY THE KEY VALUE CLUTCH KIT. When you talk to the dealer to get the clutch make sure they are selling you the individual parts (the one you want doesn't come in a kit)...you want the original equipment, not nissans aftermarket key value kit.