UpperRegister, AO Smith is a good manufacturer of many plumbing fixtures. We frequently specifiy their stuff for our building projects and have had excellent results.

Heated water can be corrosive to certain metals when stored. Most HW heaters have an anode rod ( a metal alloy rod that reacts with the heated water to help balance the ph) that needs to be replaced evey 10 years . This varies depending on a lot of different factors, it's not uncommon to get 20-30 years out of a decent HW heater but some only make it to 10 or less. Sediment that makes it past your pump filters and gets into the tank can also degrade the tanks internals and cause premature failure.

$700 bucks for a new tank, installed with warrantee is a pretty good price, especially if you can get another 10 plus years out of it... a small price to pay for comfortable showers.. The only way you will get it cheaper is to do it yourself but most manufacturers will not honor a warrantee unless it was installed by a licensed professional. I would also stay away from the gas connection...... some things are better left to the professionals.

Some gas companies offer a small rebate on energy costs if you install a high efficiency gas appliance in your house.. It's worth the phone call to find out. They may also have programs for replacement of older, less efficient appliances where they help defer some of the cost. Good luck!!