Well first browse through Ac Propulsions web site if you haven't. There's some cool stuff there. The selection of lithium ion would be simply for maximum range. The Nickel Metal Hydrive equiped EV1's range was about 140 miles with their ultra efficient drive train. The Tzero can go about 300 with it's lithium ion pack. If you didn't need extreme range nickel metal hydrides would probably make a lot more sense as far as cost, and they don't have the issues of lithium.
Another promising solution is nickel zinc, which would give you about a 100 mile range and not cost an arm and a leg.
If you just wanted a get around town fun little mini conversion though you could do it with some Hawker batteries probably fairly well. As far as price, well... the EV components for a good conversion would run probably about $10,000 (I know eww), but that would buy you some pretty good stuff. Check http://www.evparts.com
Wilde EVolutions has all the goodies. If you had some extra money sitting around and found say a mini with a blown engine it'd be cool.
My EV background came from my High School's now penniless and defunct electric vehicle racing team. We had a Plymouth Laser made in to a full race car and a Fiero that was street legal. Now they were limited for saftey purposes, but it got me in to the preformance EV stuff. Just to throw out a little snippit to impress you here in the Phoenix area lives the current 1/4 mile electric record holder. His dragster has ran an 8.801 at ummm, really fast, I'm not exactly sure, but he had to tone it down at one point so he didn't have to pull his chute (I think he's crossed the finish line at 149mph, they want a chute at 150 if I recall correctly).
But yeah, I'd have probably never known about the Insight if it wern't for the club at school. But at heart I'm an EV guy, certain things prevent me from driving full EV right now, but I'm possibly working on it. My dream car, GM EV1, no doubt in my mind. Too bad they are all going away. Here it is, I'm saying it, if somehow someone had an EV1 (with a title) and came up to me and asked if I wanted to trade I couldn't get rid of the Insight quick enough. I'd say here's my keys, whats the activation code? And drive off with it without a second thought about it.
All well, I at least have my GEM car for my short distance neighborhood commutes. I've had it for about two months and have put over 150 miles on it so far.