that explained a lot...But i have no experience with conversions and have only read about then...)
As others members said, you can't beat the price, the quality and the reliability of a used EV car like a Nissan Leaf.
They have been designed by thousand of experimented engineers and built at many thousand of examplars. How can you think to beat that with cheap chinese parts and no experiment?
You can build an EV for fun, to learn or to have a unique project, but not to save money*.
Your idea to put more EV on the road is good, but you will need to figure out an other manner than conversion to reach it.
*Except by building a poor quality EV or by finding really cheap used OEM EV parts.