if this is what i think it is, a radom 9mm, there are about 4 different grades. the best is the grade I, made from 1935 (or 36, can't remember right now what the first year was) to 1939. these had the polish eagle on the left side of the slide and the year it was manufactured. the '37 was the rarest, '36 2n rarest. the '39s had mismatched serial numbers on the parts from the factory. from then on, they were made for the nazis (because the nazis ran over poland and took over the factory). these have the left side marked with 'F.B.RADOM VIS MOD.35 PAT.Nr15567' followed by a nazi proof (eagle over 77). these fall into 3 grades, the earliest ones being the best, the later ones having lousy fit and finish and no takedown latch.
generally, if you have only 2 levers on the left side, this is a cheaper version. (nazi) ~$300
if there are 3 levers on the left side and it is nazi, ~$350-$450
if there are 3 levers on the left side and it is nazi and it has a stock slot, with good finish ~$450-$550
if there is a polish eagle and it has a stock slot, with good finish this is worth more depending on the condition.
the most accurate way to get the value is to get the serial #'s and check in a book for the grade. i can't remember now what the serial # blocks were, but they are the best way of nailing down the exact model and then use the guns condition to adjust the value.
a good place to start is the auction boards. gunbroker and auctionarms regularly have a few up for sale.
i have a matching '36 in excellent condition and was offered $2000 for it by 3 different dealers. if it is in good shape, and you know some of the story of how it got here, get it and keep it. pieces of history like that are disappearing. i knew the vet that brought back the one i have. he told me where he got it and left it to me when he died. that's worth more than a couple of bucks. if you can, send me a pic and i might be able to help you.