I'm a Handyman, Home Remodeler and General Contractor. Most of the water heaters that I replace for clients are hourly, but if somebody was to insist on an upfront price for labor, $250 sounds pretty fair. I have to go into it thinking about what will go wrong and guessing how long it will take me from the time I get there to the time I leave. Hourly is more fair, but some people don't like the idea of know knowing what they will have to spend before it happens. I have to take into consideration a lot of variables before I start in order to make sure I'm not losing money by taking on the job. Will I have to get more parts? Will there be a code violation that I have to correct? Will I have to remove, rebuild or replace anything in addition to the water heater itself? Will it drain all the way and what will it weigh once drained?
For me, I give the price and it's a take it or leave it situation. If you don't want to pay me what I feel my time is worth, then I'll just go on to the next job where that person will. There is too much work out there to work for less and too many people waiting for me to get to their job to do one for somebody wanting me to do it for less.
Finally I wonder what you would charge to go to somebodies house and replace their water heater? Not a neighbor that you know, but a total stranger that lives half an hour or more away from you in a house you don't know anything about for a person you have never met? At $50 an hour, would you commit to one hour pay before you got there? What would you bring with you in your vehicle and what would you do if you came across something that you saw was wrong with the way it was installed before?
I've seen gas water heaters vented into the attic and black charred wood on the roof decking. I've seen pressure release lines that where clear quarter inch tubing, thin wall pvc and garden hose. I've seen nothing on them and I've seen them going straight down into the pan. Rarely do I see them going outside to a safe place to discharge with a 3/4 inch copper of PEX line. Some don't have shut off valves on the water lines, some are sweated directly to the water mains and some have valves that leak as soon as you turn the water off.
Eddie