This is a house-brand bike from the Performance Bike shop chain. Made by a 3rd party, and sold only in Performance shops/ catalog.
House-brands, from shops like Performance, Nashbar and REI, are considered to be 'value' buys, retailing for less than a 'major brand' like Giant or Trek, at a similar spec.

A quick google turned up an M-407, and 307, from 1998, or so; I'd say your M-207 is the next rung down the model ladder. So, is it rare? Yes, there proabably weren't many of them, and fewer have survived the last two decades. Valuable? Not really. There's not much market for 20-year old, low-end FS bikes.

Even high-end MTBs from 20 years ago are obsolete, but that doesn't mean they're not good bikes. For $10, if all it needs is a seat, you practically stole that bike.

Take another picture of it during the day, and we can get a better idea of what you're working with.