For a Favorite that's 'all there' and in decent mechanical condition dispite a poor bore, I'd put $150 on it at a show in hopes that another person like me that likes project guns comes along.
The caliber is a downer but they are convertible to 22rf if you are again the type that likes to tinker with these. Conversion of the block to 22rf from 25rf or 32rf is just one of the many things that's commonly done to these.
Even when all rebuilt,,these are 22 std vel only guns. They will shoot loose with HV ammo as only the linkage pins support the breech block,,not the frame walls.
I've seen some ammo for the 25RF made from industrial 25rf blanks but I wouldn't want to go there especially with a Favorite action. They are quite frail as they are.
There are 3 or 4 types of the Favorite action.
If it happens to be the early small 'Sideplate' action,,you have quite a find!
In most any condition, a collector/restoration 'smith would pay a good amt for one. The last one I had was in the late 70's and resold it then for $500. As the name says it has a large separate side plate cover on the right side of the frame to access the parts.
The Model 1889 is not often seen, Flat mainspring and 7 oclock extractor. rounded frame contour at the corner of the standing breech. Bbl date is '89 IIRC
Model 1894,,the most common. Bbl dated '94. Early ones have 7 oclock extractor, quickly changed to 6 oclock. Same frame style as the 89 & flat mainspring. Looks alot like the 1889 model.
Lots of different configurations, rd and oct bbls, part oct. Most have a simple block fixed rear sight. Lever droop common on these as the action pins wear quickly and the breech block doesn't actually seat against the frame at all. Early ones are better in that respect and had a small screw down in the action accessable when open,,tighten the screw and it placed pressure against the link to remove the droop problem. The Model 44 used the same.
LAst one was the Model 1915,,usually marked as such. Thicker action frame,,squared frame corner contour,,this one uses a coil mainspring set up. This one the least desireable of the Favorites,,or at least it used to be simply because of the coil spring and less than svelte design.
Look for cracked tangs where they join the frame. A common problem,,and they do not weld very well. Brazing or silver soldering was a common fix. There's probably a weld application now that works, but there wasn't much when I was playing with them.
These rifles are still very popular with the Single Shot crowd. Rebuild, reline, refinish, restore,,they are fun projects that don't take a lot of resources but still produce a nice finished product.