I saw this funny cartoon (Zits, September 29, 2011) and I got to wondering, just how much heating time would one dollar buy me here in Sunnyvale in a classroom? Of course this would depend on how cold it was and which room you're in and so on, but I did an estimate and came up with these results:

In a natural gas furnace-heated room (most of the permanent classrooms) you would get about 4.25 hours of heating.

In a "portable" type classroom with an electric heating unit, you would only get about 1.5 hours of heating (electricity being more expensive than natural gas, after all).