Yeah $400-$500 is about max I would pay for something in the 220g range. The 220g (Tank & Stand) I was getting ready to set up before I got laid off was in perfect condition, and I got it for $300.
I usually look $1 per gallon for tanks under 200g... then use that as a base when looking larger. Obviously some of the extremely large tanks, or custom jobs command more, but I don't really consider a 220g tank in that group... maybe on the fringe if anything. I think $400-$500 for a used 220g is very reasonable.
One thing I will say, if you have a tank set in your mind that you want... I wouldn't settle for less... unless you got a heck of a deal you couldn't pass up.