There will be nothing that will work in the consumer end, and business radios will need a network of repeaters. You will get about 1 to 2 kilometers at most, even with the best handheld radios.
I am assuming there are no communication companies who rent two-ways and have a repeater network in that area. What about any local Ham radio operators or Ham clubs in the area? In a single event such as this, using volunteer community help, local Ham radio operators are invaluable.
This is how we communicate at our international marathon event.