It is my understanding that the more expensives ones, within a same product line, are just better insulated. You would get the same result (possibly even better) for less money by wrapping a batt of r20 insulation on the unit with a blanket.
Do check that the other features are the same though as there can be differences in tank composition or anode that would affect durability.
I paid to have mine switched from gas to electrical since I needed an electrician to install the 220V circuit, but there is no way I would pay again for a straight replacement. It is a simple install, probably less than 30 minutes if you are a bit handy.
I paid about 900$ for a 60 gallon tank, including the install.