Your question does not include if there are any german military markings associated with this P-38 pistol.That being said and the high serial number,I would assume that it was made after 1945.It could be made by Walther any time there after.You may want to contact Walther directly and see if their customer service dept may be of some help.
5000$
You will need to contact Walther to find out.
1961
Yes.
Someone at the p38forum.com might be able to help you.
Try posting at p38forum.com
http://www.p38forum.com/
Dieter Marschall's book on Walther has sn data in it.
There are 3 dates that your Walther P38 could have been made.If it has a date of AC 1942,then it was made in december 1942.If it has AC 1943,then it was made in september of 1943.If it has AC 1944,then it was made in november of 1944.
Try asking on the p38forum.com
100-1000 USD or so
Try the P38forum