So, is that a vintage MTB with 26" wheels, somewhat like this one:
or this one?
Probably 1990's or early 2000's MTB, 26" wheels. They often take a bearing in value. I'm seeing asking prices in the range of $300 to $550. But, those prices may well be a bit on the high end.
As mentioned above, there are a lot of details about the exact construction of the bike. So, we'd have to know about YOUR bike. Shocks? Anything that has been changed or updated?
Maybe $200 if it is something that you really want???