$80 for a working model 80 is a bargain. You can't go wrong at that price and condition.
I have a model 81, the tube magazine version of the model 80. I also have the Glenfield model 25, which is the same thing as the Marlin 81. Marlin and Glenfield made these rifles for a long time. They are all good rifles and there are plenty of parts and magazines available for them.