Really need a bit more information.
If it is 85% ORIGINAL finish, has ALL matching serial numbers, correct grips, correct eagle-over-135 waffen marked magazine, no import stamp, and no holster, then the value is probably in the $650-$850 range. Closer to $650 with nicks and dings, closer to $850 with nice metal. Locking block needs to be in-the-white and correctly serial numbered to the gun. The barrel is assumed to be VG-Exc. A bore that looks like a sewer pipe drastically reduces the value.
If it has any of the detractors above (mis-matched serial numbers, import markings, incorrect grips or mag, etc.), then it is just a nice shooter with a value in the $400-$500 range.
Add $100-$150 if you have a correct 1943 P.38 holster in decent shape.
Last week I saw an all-matching Walther ac-44 P.38 in 95% condition go for $570 on an internet auction site. On the same site I saw a Mauser byf-44 P.38 in similar condition go for $1,750 but it was a Nazi police Eagle-L gun that is much more rare than your common Wehrmacht issue. I thought the Walther went too low and the Mauser went too high. I guess ultimately the value is whatever someone else is willing to pay...
-Lee