How much does this banjo cost?

My grandmother gave me an old banjo she found in some ancient family storage, its in really nice condition, the only noticeable wear is a slight discoloration of the... head cover? I know its really old, probably from the 1920's, and the only identification it has on it is "MB75" on the back of the peghead. Any extra information anyone might be able to give me about this banjo would be helpful, cus I honestly have just no clue where it came from or anything.