The way I do my budget on these electric conversions is simple, how much does it cost if I were doing it as a gas engine, and can I match that!
Oh ya for sure some of these guys are spending some money, for me it's a shoe string budget, heck the electric Massey has got more $ in it than any of my others. Power, big motors, lithium ion batteries, cost, unless you can stumble across them somehow.
Then I price all the materials and look for the best prices on the best equipment and I always get the motor first, controller last. But I go through lots of math and stuff to calculate how long it will last. The Electric SF was a used motor and I questioned if it was too small, but decided I was crazy... but then realized.. I was right, dang lol. So my conversions are really to have a little fun for myself and then to show people that for about the same cost as repowering with gas engine I can convert to electric. I think more people will convert if they see just how cool you can make it for similar cash!!