Having it nickel plated pretty much destroys any collector value for the gun.
Lots of really (potentially) valuable WWII pistols had that done to them, and ruined them as collector pieces. (I can't tell you how many nickel-plated and chromed Lugers I've seen. They sell for $500 - $700, at most -- although they're generally price much higher. Priced at, and sold at, are two different thing. Had they been left original and kept in good condition, they could be worth 2-3 times more.)
As noted, a picture would help, as there are a number of collectors who participate here.