Nuthin' Magic About It...
I worked with propane extensively as a forklift mechanic and currently work on very large CNG engines and compressors for the nation's largest clean air fleet. Don't expect to become a genius on the subject overnight but with a little research you'll find it's not so intimidating.
Actually, Natural Gas IS put in cylinders. For light vehicles the limit is 3,000 PSI. For large vehicles the limit is 3,650 PSI. We can fill a 60 foot articulated bus in 5 minutes or less to 3,650. Fuel milelage sucks (natural gas, or methane, is the lowest BTU value of all alkanes, having only one carbon and four hydrogen atoms) but it's very clean. It can be rough on spark plugs and requires a special low-ash oil because the fuel has no lubricity.
Propane, having four carbon and ten hydrogen atoms has enough lubricity to work with conventional (read: affordable) oils. There is generally a 10% reduction in horsepower and torque over gasoline but it does burn pretty cleanly.
Converting back to gasoline gets more complicated on newer vehicles. If the car was originally equipped with a carburetor it's a relatively easy (though potentially costly) task. Originally fuel injected/computerized? Not so easy, very costly.
How badly do you want the car?