Your tuner may have been "kind" to you. Loose pins usually signify a larger problem. If they are close together in a line, it usually indicates a crack in the wrest plank. If they are distributed throughout the pin block, the block is drying out. Sometimes a tuner technician can solve the problem with a chemical rejuvinator at the pint; sometimes just a larger diameter pin.
It generally doesn't matter "how old" a piano is after 75 years. At that point it's due for rebuilding, this one may have already had a bit of rebuilding work done. Felts and keys are a start, but often fail to address larger issues of strings, bridges, soundboard (and pin block).
The fact that the piano was painted (twice) does't sound like it's had a very nice life. Maybe it was in an elementary school environment or someones basement.
I couldn't tell you if $100 was a fair price for it. Probably, but I wouldn't spend a whole lot more on it; Bher Bros. wasn't the end all-be all of piano manufacturers -- nice but not great. As a late 1800s piano it may have some nice cabinet work under all that paint that could be restored, but if there are missing veneers and turnings it will be hard to duplicate. The appeal as a restored instrument will also be focused on people who love antiques.
Edit: Behr Brothers. was a New York city manufacturer.
I'm assuming this is a tall upright about 52" (possibly labeled "Cabinet Grand")
Edit 2: If you enjoy the piano, and the piano is in essentially good condition, then keep it and ship it (adding it to household goods isn't going the change the cost of a move too much.) This could be a case of better to keep what you have and know (and refinish externally as needed) than to try and find a piano in similar shape.