I haven't ran the figures recently, but the "rate" on leases is much higher than purchase. It's not considered an interest rate, because it's not a formal loan, but it works the same. When I last purchased I crunched the #s and that rate was about 3.5x what the rate was on a purchase loan.
One option to consider.... certain banks/credit unions offer loans that act like leases. They calculate the estimated depreciation, and your payment is so that the only principle you pay is that depreciation, so the payment is much lower than a standard loan. At the end of the loan term you face a balloon payment, at which time you either refi the balance or you trade the vehicle. So for example, if you do a 40k loan for 3 years with and estimated depreciation of 18k, the 36th payment (end of the loan) will be for $22k.
Note - you are also charged interest but on the entire loan amount.
If you plan on buying the vehicle at the end this is a good option because you own the vehicle - you don't face mileage restrictions, and the rate is much lower. The down side is you are stretching those payments out for a long time.