Please check with your local plumming supply store. It is a published national average for tank water heaters to last about 10 to 15 years. It is has nothing to do with my local gas prices or my water supply. You show me where you can buy a high efficiency power vent 50 gallon water heater for $250. If there is one, I definitely would not risk my family and my house by putting in a cheap water heater that could put CO2 in my house or rupture. When it comes to the safety of my family, I'll never go cheap. And, I'd never recommend anyone else do so.
Again, there was basically no difference in price for a high quality tankless water heater vs. a quality 50 gallon power vent tank model. And, it may not be much for some people, but for each tank water heater I replaced, I saved roughly $20 per month on my gas bill. To me, for the same price, unlimited hot water flow, longer life, and noticable energy savings, I'll still go with a tankless every time. But, that's just me.