A really good GI bring-back unmarked by an importer will certainly command a much higher value than a recent import rifle. You might check on Jouster.com or Gunboards.com (both have Mauser forums) and see what the exspurts have to say.
Besides some real monetary value, this rifle has serious sentimental/family value.
There are so many factors in the military Mausers that it'll take a truly knowledgable collector to pin down a good monetary value.
PROUD TEA PARTY EXTREMIST!