We've got Reflecto-ray tube heaters in our shop. They're about 16yrs old now and the only problems we-ve had is the primary control going dead on a couple of the burners. Standard Honeywell control part, available locally, and took about 10 minutes to replace in both instances. They should be piped to draw combustion air from outside, both from a safety and an efficiency standpoint. They have to be set up properly to control the negative pressure within the tube, but that's part of the initial installation, and doesn't require adjustment over time.
Radiant heaters heat solid objects instead of heating air. With gas fired unit heaters, or some similar warm air type of heat, the air temp can be 70 and you can still feel cold if you're working near a large machine that's colder than the surroundings. Same effect as sitting near a large window when its cold outside, and feeling warmer by closing the drapes. Any warm object, including humans, radiates heat to colder objects. Because radiant heaters heat the machinery and the floor, you find the shop temp can be set several degrees cooler than with warm air heat. We keep ours at about 60* and you really wouldn't want it any warmer if you're moving around any at all. We can have a 14'H x 14'W door open for 5 minutes when the outdoor temp is well below freezing, and within a couple minutes of closing the door you can't tell it was opened by the way the shop feels. Doing the same with warm air heat can leave the shop cold for an hour while the heat system recovers the temperature.
The highest gas bill we've ever had was on the order of $500 for a month, for 7500 sq ft of shop and 1500 sq ft of office space which is heated by a condensing type gas furnace. Metal building, well insulated, built in 1990. But, we've got 6-14x14 overhead doors, and the fit of those doors probably accounts for $100 of the gas bill in a cold month. Previous shop was 5000 sq ft with warm air heat. Gas was cheaper back then, but the gas bill there would run $800+ in cold months while everyone in the shop was still bundled up and half frozen most of the time.
In some areas the gas company will furnish and install tube heaters for about what you'd pay just for the equipment from other sources. They do it to add to the customer base. Don't know whether propane suppliers offer similar deals or not, but its worth checking out.
added: You've got to have fairly high headroom to use tube heaters. Our buiding has 16' eave height, and once the heaters are dropped down to give adequate clearance on the top side, the tubes are about 13' off the floor. Works fine, but you wouldn't want to put them in a building with 10' ceilings. The manufacturers give info regarding minimum mounting height and topside clearance, and you can't really cheat on either dimension without becoming either uncomfortable or unsafe.