4.5" full size, I saw them going for under $600 with the full Springfield xdm kit brand new at the gun show in Indy last weekend. So I wouldn't pay more than $500-550 if it was minty.
For the 5.25 comp. version, they're about $100-200 more than the "full size 4.5" version.
I've bought 2 5.25 in xdm 9mms and one I paid 600 for the other one 650. They are generally pretty close in price.. The smaller models are 550-600 when I've seen them.