It depends upon several things, most importantly condition. There were several variants over the lifetime of this gun. Some of the earliest might be hard to get parts for and it takes special tools to work on the seals from what I understand. Most of those you see for sale invariably say "Will need to be resealed". Brian and Associates are the people to rebuild one.
So, does it hold and shoot and, if so, how hard? These will be about like a Sheridan Blue Streak, maybe a tad less power. What shape is the stock and metal in? Which vintage 101 is it? Some are considered better built than others.
The best place to look for info would be the American Vintage Airgun forum. You can ask there but there are also some nice links in their library section. You know, I think I'm gonna have to get one of these.http://www.network54.com/Forum/405945/
Oh, yeah. As to value, for a run-of-the-mill "5 ring cocking nob" model that is holding air and has maybe 80% finish left, about $125 or so. Again, as they say, condition is everything.
PS - The Vintage link to the library is in the "floating" links box in the upper left portion of the screen, top link. Takes you to another page and then I think you have a link to the library. Look for the Crosman 100 series article.
Here's another - http://www.pyramydair.com/blog/2005/12/crosman-101-multi-pump-pneumatic.html