This isnt always the case. I have helped build a few electric conversion cars You can use cheap lead acid batteries and still get some range ( a older porsche 914), 8 lead acid batteries and a forklift electric motor, car can go almost 100 miles on a charge and the most expensive thing was the controller.

You can also buy battery blanks, where you add the top to them, (think AA style) then put the shrink wrap on them and join them together to make a larger battery, they allso do this for battery backup for your home. Lots of labor, soldering etc...

This is very quickly evolving industry / technology, and i am sure one day I will build one for myself, just not yet. I want to see some better battery tech come out. Really if you think about it, serius bnatteyr research has honestly only been going on for maybe 10 or 15 years, Think of an internal combustion engine (ICE) 15 years after devlopment... Not very impressive compared to todays ICE engines.