Reg fee. Too long. Most vacationers or travelers to even panama are most likely to book a car rental through their travel agent or go direct to know car rentals like Hertz, Avis, National, etc. Either that or thought online sites like Orbitz, Expedia and more that offer flights, hotels, auto.
I think most people will want to solve all of this issue with one or two sites.
Placing a city to it also restricts the market and shrinks the market.