Oddly enough, our hot water heater was just replaced, today. We have been without hot water since Wednesday, which has been interesting.
First of all, we have a home warranty. It is less than $500 a year and our AC could go out at any time and we have some various plumbing issues. With the plumbing issues alone, we have already saved money on what we paid.
So anyway, if it was a smooth transition, it costs us $60. New water heater and labor. However, there were other issues with pipes and Co2 stuff (gas heater) and vent thing (sorry, I don't speak water heater..). Including our $60 warranty payment, our total was $400. I know that the heater is in around the $300 range, and I have no clue what labor costs for the heater instilation would have been. They were here for almost 4 hours with all of the issues.
Oh, ours is 40 gallons (we have a seperate tankless heater for our laundry) and it is in a closet (we live in a ranch style), but our home is pier and beam and the access is also in this closet so the heater is on a shelf that is about 2 feet off of the ground. I felt very sorry for the plumbers.