That seems high. I would shop around - I know at least one of the large area plumbing chains has given me insane estimates ($740 to replace a sink shut off valve and repair a leaky pipe- I shut off the house supply for a day and waited for our local plumber to come- $150 job)
the old gas hot water heaters with a bottom element heating a large tank of water are largely obsolete thanks to regulatory changes a few years ago requiring only the manufacture of high efficiency models. If you can still find one of the old ones the installation price should be closer to $1200. If not, $2500 is about right, especially if they need to run electricity to the unit to power the internal motor. On the plus side, the new units are far more efficient and cheaper to run. On the downside, the efficiency gain will likely never pay for the additional cost, and because they use electricity, you won't have hot water if the power goes out (unless you have a whole house UPS).
more info here:
https://www.washingtonenergy.com/idea-center/2015-government-changes-water-heaters-will-affect/if you are anywhere near Manassas, VA, I strongly recommend Air-Right HVAC services.
