Thanks to Quicken's excellent memory, here is my record. I replaced an old 40 gal. water heater with a new 40 gallon one (LP gas) in 2008 for exactly $925.00. The work was done by Better Water Heaters, FWIW. I only helped the installer to lift the unit. This includes the cost of the new heater, and all the labor, and removal of the old unit.
Specializing in waters the companies usually come in a little lower, because they go for production, and water heaters are a nice little niche to focus on.
That price would have been close to, but a little under what most full service plumbing companies would have charged (on average), and it was about right for 2008.