Barry, I've got another out-of-state driver who might be interested. He's got lots of experience travelling around the country doing silly motorsports stuff. (autox, hillclimb, open-road racing, etc) Obviously, he won't be available to help prep the cars, but if the schedule works and he can make it to drive... what sort of contribution would you ask of him?
Along the same lines, I'd suggest you budget this. Yeah, you've theoretically got a $500 budget for the cars. Even if you spend and document $500 on each of the cars, they won't believe you, anyway! So, don't get too wrapped up in that... but don't make the cars look like you spent thousands of dollars on the, either.
Budget for entry fees, tires, gas (and oil and other expendables that don't count toward the $500), the cost of the safety equipment, etc. I think you're going to want/need to collect some cash from each fo your drivers to cover the expenses unless you come up with a big bucks sponsor.
Also... I'd be a proponent of running the same engine in both cars. "To finish first, first you must finish." This is an all-out violent endurance race. Stuff is going to happen, and having a nice pile of interchangeable spare parts would be a very good thing. Probably more valuable than the extra HP.