Franchise operations are costly. You have to sell more coffee than you can imagine to pay for some franchise costs. Do the math carefully. You have overhead, materials, payroll - but how many cars can you serve per minutes? Figure the average ticket take and see if you can really afford to pay for all of the above AND support someone else's "dream" design. You really have to ask yourself what exactly you are getting for the price.
I suggest you talk with a local roaster about supplying the coffee and contact an equipment supplier about equipment and training. With a little marketing you can probably come up with a better design than what you will pay $25 to $30K for.
There are a lot of resources out there than can come together to get you up and running. In the end, the cash is YOURS and you won't be paying for someone else's idea. Just my thought - I've had a couple of customers that started out with the idea of buying a drive-through coffee franchise and end up doing their own thing.