The problem with Propane is that the car will be alot slower than on gasoline. Propane contains alot less energy than gasoline. Natural gas is even worse. Also, a propane powered car will use alot more fuel (litre) than on gasoline. The offset in total price is only worth if it's a fleet car. For example, if your car uses 10L/100km on gasoline, it will use 13 or even more on propane.
The last time I checked into the conversion was 10 years ago and it cost around $2000. By the time you break even the car will be a rust bucket.
I would only convert a large V6 or a V8, nothing smaller. Best way to get one is at a goverment auction. They sell these cars for next to nothingt.
