I have connections and i get it cheaper than 1.40, but not a lot. As far as i know, nothing has been modified on my engine except the addition of the propane system. And a straight fan, no clutch. You also didnt mention carrying around 72 gallons of fuel.
Your biggest outright expense is parts. Tank, hoses, vaporizer, lock off valves, and of course the propane mixer. I run an impco 425.