I agree with Volker, it's difficult to compete with the mass produced versions after incentives. Without those incentives, a DIY conversion can be much less, but with them most small EVs sold are within a few thousand of conversions.
Not what I have experienced. The EV meetings I go to are peopled by engineer types who have spent hundreds of hours making their gas baby into an EV. When they are done, they have an electric car with low top speed (70 mph?) lousy regen if at all, heavy batteries, low range (30 - 50 miles), and a persnickety charging system. Their wives get stranded because something blows when she borrows it. The rest of the group are poor wannabes who keep thinking that they will be able to convert their 69 Ford Falcon for a few hundred bucks and be able to drive it on free public charging. In every case I have seen, you get what you pay for, *IF* you're lucky. Always you end up with an old car with out dated safety features, poor driving characteristics (due to heavy batteries installed where they weren't designed to go), bad wiring, rusting body, repaint, etc., etc.
I have acquaintances that think that conversions are the holy grail. I don't think so. Conversions are so much less than any other commercial electric, it's hard to compare. Oh, sure, once in a while, if they're careful, someone will get 100 miles on a charge, or have a classic auto that still has appeal, but that is in the infinitesimal minority, IMHO. People building cheap cars (conversions) notoriously use lead acid batteries, and they forget to tell you all the fun you get keeping them watered, charged up, and then replacing them every 3 years. They can't afford NiMH or Li Ion, because the government, or some business group, has priced them out of the market for the small user. Yup. That's what they do.
No thanks.