Well, the cost of my conversion can be split three ways:
1) "donor car" cost
2) classic car restoration
3) Internal combustion engine (ICE) to Electric vehicle (EV) switcharoo.
1) I paid a bit more money for mine because the previous owner has already sunk a few thousand dollars into the car, partially restoring it and souping it up to be an 18 year old's daily driver, if you know what I mean. There's a father-and-son team who I'm helping with their project right now, they paid $500 for the 914 off of Craig's list. They've got their work cut out for them. Pun intended. Like cutting out rusty metal. But if they're having fun and bonding (& bondo, too) more power to them.
2) It's common knowledge that classic car restoration is like pissing dollars down a rat hole. Only in rare occasions do you get your money back should you sell it. I'm not a Porsche purist, by any stretch of the imagination, but parts, even imitation ones, are still pricey.
3) If you already have a car and am happy with it's looks or condition, this can be done well under $10,000. I've seen conversions that look like POS. Duck tape visible, wires hanging all over the place, redneck repair with WD-40 and JB Weld, crap all over. But then owners are hippie types in tie dyes, so everythng's cool. Dude.