The price difference will be big if you are shooting on K40 versus any 16, but remember that K40 is reversal intended for home movies.
To be honest it is a great way to start because the film and the processing are so cheap. But if you are looking for soemthing that will come close to comparing to any 16, you are going to have to get pro stocks cut down to 8mm. Such as at pro8mm.com. I am in Seattle and some local places also have kodak vision and other stocks cut down to super8mm. They are more expensive, but will yeild much higer results after telecine. Pro8mm have a demo DVD available. But even after seeing it and looking at the not so great price difference between the highest end 8mm and 16, i have chosen to shoot my first film (next week) on 16mm.
If you are a film student you get a 20% discount on all Kodak and Fuji motion picture films. If you are a student but not in a film program you cannot get kodaks discount but you can get Fuji's. Its working great for me.