If you're paying over $60 for a burner motor you're getting ripped off, not to mention it's at most a once/decade expense.
If you're using a non-condensing gas boiler with its less complex controls you're going to be getting less efficiency than your standard oil boiler. Oil can run higher efficiency in a non-condensing appliance. What this means is that if you're running the simpler, far less costly (than complex condensing propane boiler) cheaply controlled propane boiler, your fuel costs will be even higher with propane to get the benefit of less complex control.
Solution: Use oil, keep the heat in your name, charge flat fee or build into rent heat, install dummy thermostats in apartments; set real thermostat in air return (not possible w/ boiler system unless there's a hydro-air zone) or relatively inaccessable common area and set to 68. http://www.landlordstat.com/product/hc7 ... o-setback/