it's not bad . . . i paid $400 for a 75 gal, with coralife lights which includes lunar lights. i also got a stand and glass tops and a fluval 405. he wanted $500. i negotiated $400.
I got my 150 tall with stand, dual 48'' lights, 2 Emperor 400 for $350. I wouldn't pay $550...though that is a standard 150 and the stand isn't the metal type like mine so I might pay a bit more but see if you can get him down...it depends on what your willing to pay and if its in great condition or just ok condition