If it is a break top it will be a 32 S&W caliber. A very underpowered round. Think a 75 gr bullet going maybe 600 fps. It all depends on what you intend to do with it. If it is a very clean and you want it for a collection or display, that is a decent buy. If it has lots of wear it isn't so great a price. If you want to actually shoot it, be prepared to spend lots of time just trying to find ammo, and when you find it it will be very expensive.
As the gun could be from 90 to over 130 years old, parts are not easy to find if you break anything. If you are thinking of it for a self defense gun, please get something else. I am not trying to discourage you, as the picture shows, I like them (as collectors items) I don't shoot them.
This is a 2nd model, called a Bicycle gun.
This is a 1st. 2nd, & 3rd model Safety Hammerless.