There are several variations to the post war P38,s. The ones made in the late 50's and early 60's do not have the reinforcing stud common on the later ones to make them hold up to hotter 9mm NATO loads.
If its actually marked P38, its worth more and hence worth the 300+. If its marked P1, its worth a bit less around 250ish.
My P38 was made in December of 1961, has all original parts and still shoots like a champ. These were a great gun and I wish they still made them.
Just so you know when you go for a WW2 one. Stay in the 144 or earlier range if possible since some 1945 production ones have some metal fatigue issues in the safety mechanism. Also the Spree Werke guns are the worst so try to stay wawy from the CYQ production codes. I find that the AC code (Walther) and BYF(Mauser) codes are much nicer, with the 1944-1945 Mauser ones being nicer.
There are some SVW codes out there which was late 1945-1946 made under French occupation. These are also two tone and are known as the Grey Ghost P38s, and are just fine sicne they werent rushed.