Under 100,000 miles the cost of replacement will be $0 as it is covered by dealer warranty. After that the battery will run between $2400 to $2600 depending on the year of the vehicle. You also need to consider in the labor to install it unless you replace it yourself!
Typically it cost about $2,299 for a first generation model and only $2. 588 for a second generation. That is for a dealer replacement and doesn't not include the computer that often need changed. This can add another $3,000. Some people have had a mechanic just change of the old cell for a considerably less amount.