That's a pretty good deal for the commemorative edition gun. Regular Buckmark Camper models with cheaper grips and shorter, cheaper barrels are just under $300 new. Those grips are worth $50 easy, and the barrel is kinda nice too. It also has a little nicer sights and a real metal sight rail, unlike the Camper model. Of course you could get the same functionality without the engraving or the grips for abouty the same price new.
The Buckmark is an excellent rimfire auto, and parts are readily available from the manufacturer. There is also a ton of aftermarket support. And yes, the barrels are interchangeable...