For people interested in converting their vehicles to propane, there are many conversion centers around the world able to do this work for them. Carbureted vehicles are the easiest to do but modern fuel-injected vehicles are pretty much the only ones being done today. The DIY mechanic generally does not have the capability to do this work which then requires him to find a licensed conversion center. Conversions in the USA require EPA-approved systems as well which limits the work a do-it-yourselfer can realistically do.
In Ontario, there are a number of facilities licensed to convert vehicles. Since conversions are typically done on fleet vehicles, popular vehicles for taxi and limousine service are the Ford Crown Victorias and Lincoln Town Cars. A good conversion of such cars will cost in the neighborhood of C$5000 but low-budget, failure-prone ones are significantly less. Remember, sometimes you get what you pay for, so caveat emptor!
Before you inquire about doing a conversion, you should look for propane stations in your normal driving area and see if propane prices are significantly less than gasoline prices. One of the cheapest places for propane in Canada (which implies the greatest difference between the two fuel prices) is in the Toronto area, especially near Pearson Airport. This is due the convergence of fleet vehicles in this area. Ask taxi drivers where they buy their fuel and you will easily find the cheapest filling stations.
Because propane has a lower volumetric energy density than gasoline, your car on propane will use more fuel. You can conservatively estimate that your car on propane will have 75% of its gasoline mileage or use 33% more propane than gasoline. With your total estimated annual driving, your should be able to calculate the amount of propane you will use annually and then calculate the number of years the conversion will pay for itself.
Converting modern vehicles to propane operation is slightly more involved than converting older carbureted vehicles. Because their onboard engine management systems are so integral to the operation of the vehicle, you just can’t pull the injectors out and bolt on a propane system. As a result, these vehicles are almost always converted to dual fuel operation.