Literally anywhere that sells water heaters, that isn't also installing them.
Homedepot, Lowes, etc.
$500-550 gets you a 40 gallon with a 6 year warranty. Another $150-$200 gets you a 9 year warranty.
Loll actually just checked Depot has a Reem 40 gal with 12 year warranty for $639
Cost of Water Heater Installation
The national average for tank water heater installation is between
$906 and $1,583
for the
unit and labor
?huh?........ it's just a box.