I think it boils down to what one would consider a "rust bucket". The Geronimo mentioned earlier is certainly a no frills twin trainer. But it still manages to have a paint job and glass that is less than two years old, as well as a brand new Garmin 430W. Which in my opinion isn't bad for a 1960's trainer. As far as I'm aware, it is the only twin engine trainer that does not have any AD's on the airframe. While she may not be the prettiest airplane on the ramp and may not have the cleanest looking interior she is build to perform her mission flawlessly and still maintain a reasonable price for the student/renter. Remeber, just because something is old, doesn't mean it's not in good condition.
As far as fuel is concerned, we currently pay $4.84 for avgas (the local areas average rate is $5.51 according to AirNav), and we don't charge any fuel surcharges. The fact that she only burns 9 gallons per side certainly helps the economy of our operation.