You mean this one? http://www.gunbroker.com/item/609594222
Heck of a gun. Too bad about the crack, but if it's stable or been fixed correctly someone got a nice shooter. Just my opinion, but I think that's about top dollar for that when you figure in any shipping and FFL fees. Gonna be pushing $650. Overall the gun looks in really nice shape otherwise.
A 20 in that condition without the crack would be $900 to $1000 gun, again just my opinion. Show season just underway here in NY so we will see if any changes in the market the next month or so. Just depends what's available and what people want. The 12 gauge 37 market has been tough, there's a lot out there. Supremes, not so much but price reflects condition. Seems to be a premium for nice original condition 20's right now. A nice solid rib 20 or supreme...get in line.
Still better than buying a new 870 or Cheeseberg 500.
So, did you miss a bargain. I don't think so. Fair market.