I can comment on maximum price for battery back. It was mentioned that Renault is doing this battery leasing idea and they teamed up with operator of robotic battery switching stations BetterPlace. I think best results are in Israel, and they offer variety of ways to pay for battery leasing and access to stations. They also offer ability to purchase battery, as buying a car where one cannot ever own battery is a bit risky. This is data from respectable newspaper so I assume it is right:
http://www.haaretz.com/business/chasten ... s-1.451596
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77000 NIS is about 19000 $ and this price includes numerous Israeli taxes, duties and probably massive premium to make sure that you lease rather then buy battery. I think that is also ceiling to how much battery could cost.
It makes me wonder if problems of BetterPlace are not somehow related to rather warm climate in Israel and more frequent need to change batteries than anticipated.