Just like most other products, water heater prices vary in cost from one model to the next. For the most part you get what you pay for. Most water heater manufacturers will have several different models that vary in price. Along with price, the water heaters will vary in warranty length and performance.
A water heater that is more efficient will cost you more up front but should save money in the long run. Although this is not always the case. A tankless water heater is more efficient than a standard tank model but the initial cost is so high you will not make up the savings.
One thing to consider when selecting a water heater is the cost of installing the tank. If you spend $600 on a water heater and pay another $500 for the parts and materials to install the unit you have paid a total of $1100. If the tank only last for 6 years you will have to pay a plumber to remove and install a new tank. Spending an extra $200 on a tank that has a 10 or 12 year warranty can double the life. You are not just saving on the cost of the tank, you are also saving on the cost of the labor to have the water heater installed.
KC Plumber Pro installs Bradford White water heaters with a 10 year warranty on labor. Most of the warranties offered by plumbers will only hold up for about a year.