The pack is made up of 3.2 volt cells that can be anywhere from 40-100ah. You just string 45 or more together. You can add more batteries, or get larger capacity batteries. It's all modular.
Edit: I got got the price of the pack wrong, i changed the numbers to reflect it. Sorry
This is just any old battery i picked to give you an idea, You could find cheaper ones or better performance ones.
$4,687 for a 10kwh battery. If you build as efficient a car as you plan too, You could get 100 miles out of it. $6k for 13kwh would be ideal. It'd give you more than 100miles easy, a long battery life, and when the range decreases as over time, you'd still get 100miles.
These are conservative numbers though so you don't fall short in range, or expect to pay more.