IMO that chiller is going to be a bit small on a 225g. I'd use a 1/3 as a bare minimum, 1/2 preferable.
$400 for a 1/4hp is a decent deal, but not a great one. You can get them new for about $550. I guess it depends on how old the unit it, how well it was taken care of, etc. Of course all this is moot if it's too small.