Easiest way to compare is to use the money factor equivalent interest rate. Sine the best rate is 4.9% - if you can get financing for less than that, you would be better off buying. Infact, since lease has some additional costs like acquisition fee, even if the finance rate is slighlty higher, it would still be the better option.
Lease is better if
- You can't get 7,500 tax credit for some reason
- You want to buy a new car in 3 or 4 years, but don't want the hassle of selling used Leaf or the risk of a low used value for Leaf
The various calculations comparing the buy vs lease tells us how much is the "convinience" of leasing is costing us in terms of dollars.
ps : The average rates in bankrate and other places seems to be much higher than what people can get in their credit unions. My CU gives 3.4% - bankrate average is 6.22%.
http://www.bankrate.com/funnel/graph/Default.aspx?cat=8&ids=234,-1&state=zz&d=180&t=MSLine&eco=-1