The P38 is a historically significant design. All locked-breech double-actions auto pistols were copied or evolved from that design. It was developed by the Nazis, for war, a sidearm purely made for killing men. The steel-frame P38 was built during wartime, from 1938 until 1945. Every P38 has Nazi proof marks and is Wehrmacht stamped. Later surplus parts were built into the aluminum-frame P1copy from about 1957 to 1999, mainly for European police and sales to USA civilian markets. Most all P38 guns have seen combat and been fired in anger. Mine was my Grandfather's, taken from a corpse somewhere in France. It was in the first package he sent back to his bride after D-Day (along with a porcelain tea set that got chipped in transit).
Collector interest is waning, as there are hundreds of thousands out there. The web auctions show them selling (not asking) from $125 to 600 bucks quite commonly, with exemplary examples w/provenance bringing more. Lately GB is disgustingly hard to search, but the high-dollars seem to be in pristine guns with the bakelite grips, all original of course. Personally I would be very suspect of any leather holster in use-able condition, claiming to be "original" Nazi leather... Otherwise they are fine shooting guns and dependable in original, well-maintained condition.
As far as selling one today, condition is everything. If you can find the informed collectors, your selling price potential goes up dramatically (given yours is not a beater).