I just had a new 40 gallon gas water heater intsalled yesterday at my home in Kansas City. The plumber gave me an option of having him get the water heater at a price of $350 or said I could get one myself at Home Depot and he would pick it up and install it for me. I chose to purchase one from him, because he told me that his was a higher quality and would last longer (I think the brand he installed was "State"). Besides, when I looked the water heaters up at Home Depot they were not that much cheaper anyway and the plumber told me that there was even some sort of pending lawsuit against GE water heaters and I didn't want to get into that....
It took the plumber 2.5 hours to install it at a cost of $65 per hour--so my total cost for the heater and labor with tax was about $550.00. He also hauled away the old heater.
I know that things like this are usually much cheaper here in the midwest than in other places, but that may give someone an idea!
Hope that helps!