I would guess the value is from $75 to $150, all depending on who wanted it and when and where it was sold. It is a bit rough, but don't put anything on it, except maybe Hide Food by Connoly's.
Being a 1913, it is not "correct" for a Banner, so most collectors would take it with the gun, but it isn't the right years or type ( a police holster is different).
Are you selling the Banner too?
The back straps all ok on the holster? I'd be interested in the holster for a "good" price
Ed