I normally just use the hire car comparison sites and then read through the wording to see which company will be supplying to check its a fairly major company and go with that. I'm afraid I can't remember what I paid last time I was down that way
Why do people get scared about taking their car on long journeys? Do you expect that your car is going to have a catastrophic engine failure in the next 4500 miles? No, I'm sure you wouldn't still own it if you did.
All I'd do is service, check everything over i.e pads, discs etc and drive it.