I got my rear wheel (in Feb of '05) at the Monstertrack swap meet. $25 for a surly fixed/fixed laced to a Mavic MA3, with a semi decent half used tire mounted. It has never needed truing once and has had the living crap beat out of it.

So I would say anything over $50 for your rear would enter rip off territory. Could you get more? Probably. However, make a few less and pass it on to someone that wants it. Thats better for everyone.