Impossible to say exactly without more info, but not much. Jose Mugica was a gun maker in Eibar Spain who made was most known for making the Llama brand of firearms. their shotguns were serviceable, field grade guns but were built to a price point. They dont hold much value but if its in good shape could be a nice field gun if it isnt too heavy and if it balances well (this was the biggest drawback with many of the cheaper spanish SxS's) I would say the value would be somewhere between $250-$400, depending on condition, engraving, wood quality, choke, etc
