The "Blue Book" price is $475 for 100%, down to $235 for 60%. Special plating or engraving brings more. Realistically the price is what you can get; the guns have no collector value and the only value is as a shooter. Worse, they were reportedly made by different makers in Europe, with varying quality. They were also sold at one point as kits, to be assembled and timed by the buyer, so quality of any guns made from kits will be dubious. The grips (if original) are a plastic imitation stag.
Some parts interchange with the Colt SAA, but the hammer, firing pin retainer and firing pin are unique and may not be available if anything breaks.
Jim