2-hour Sterno-type cans are about a buck each in quantity and 6-hour ones are about $1.75. If you only needed one, $1.75 for 6 hours doesn’t sound bad. But they use 2 cans under most chafers, so one might not be enough. What does propane run per hour on most carts?
I noticed in a catalogue that there is an electric Sterno replacement. If you have a Sterno setup but there’s electric available, you can plug in this adapter and set it in the Sterno holder. Like all clever restaurant ideas for equipment, it was around $130. But it would give someone the option of Sterno or electric as the circumstances may dictate.