I bought a 28 nano to be used as my frag/overflow tank a little while ago. I got one that also had the stock 150 halide top as well, but decided I'm not going to use it. The previous owner said he bought it new and barely used it. It should have plenty of life left on it, but I don't know. Still looks mighty bright! Moon lights, fan, etc all work.
I'm not seeing many used for a price comparison, so I'm doing it like this: Marine Depot's NEW price is $300, so I'll sell for 1/2 price - $150.