A two barrel set like yours should be worth about $1500 if the right buyer comes along, they are a very good value for the money in my opinion. I considered buying one several times but have usually seen them offered for sale with the combo barrels only, not a shotgun set too. Decent ones were generally priced about $900 - $1100 or so, but often in .22 Sav hi power/16 ga, not as desirable for most folks. The same gun with shotgun only tubes sometimes sells for about $700-$1000.
I did see one two barrel set for sale about ten years ago, it was in the same configuration as yours but had a goofy single/double set trigger that if I remember correctly could fire both barrels with two pulls of the front, or the back was for the lower barrel only, or the back was to set the front, or some other confusing set up, and I passed on it.
They are robust and well made. But I find them kinda homely. When my search was done, I bought a Merkel set instead.