Undecided got it all pretty much right. Sail prices are a little higher. Jib 600, Main 1850, Spin I forget but I think 1500.

Great boat. And I'm not just saying that.

Things to look for on used.

Bottom screwed up from beaching.
Back of daggerboard well leaking. PITA to fix.
Mast dings or wear.
Mast ball lock mechanizm at bottom of mast broken.
Wavy or misscolored patches. Sign of damage repair.
Soft spot in front of the back beam on the top of the hull. Pretty easy fix though.

Biggest issue I've seen in older I20's is the back beam separation. But I've never seen one before they actually separate so I'm not sure how to check. I would inspect the back beams where they attach to the hull very closely.

Obviously if you can find a freshwater boat they usually are in better shape.