I've considered the infrared type heaters, but their cost is greater and I'm not sure if it would be cheaper to run?
The answer is no, Heat and electricity really do not go together as an economical heat source.. Unless of course, You are in a small electric room with 2500 amp gear in it... Even the new fangled infared ones will make the meter spin...

Most economical over the long run would be to just run a gas line to the the garage and do it that way.. If it's a detached garage, it might take a little longer for it to pay for itself.. If that is just not an option, then the propane is the next best bet.. Just make sure you have good ventilation,, Should be no problem..