When you say "Ultra" you mean the aluminum receiver Model 37 Ultra Featherlight?
When there are 5 choke tubes, I think of the Upper Sandusky OH guns, the most recent owners, where they are selling. These are better than the King's Ferry guns but not as good as the Ithaca NY guns.
The newest guns are chambered for 3", the earlier 2 3/4.. so you have to check the barrel for what you have.
The wood and hand checkering on the pre '46 guns is much nicer.. and it all boils down to exactly what you have.
Any not-rusted-in-half Ithaca Model 37 20 gauge will go for $450 on gun broker. Good condition go for $600 routinely, $750 not uncommon. When you get into the new-in-box with box and paperwork guns.. $1,000+
But then, look at the price of a brand new Fieldmaster.
I have two model '37s.. 12 and 16. Both weigh 6.25 pounds with steel receivers. I have no need for a 20. A 28 might tempt me, just because it means more trouble finding ammo.
My present 20 gauges are pretty darned nice, and there are decent offerings for $400 16 gauges which are, let's face it, the 'gentleman's gun.'