The EFI RE500 costs close to 150,000, not 115000
The trip includes airfare, which in July cannot be less than 6-7000 INR, and may go up to as much as 15000.
It also includes fuel, attendant mechanics and spares, and back up vehicle (do check out the rental for vehicles in that area for 2 weeks!), as well as the cost of transporting all the vehicles back after a one way journey.
Considering all that + obviously accommodation and 2 meals a day + services of a "babysitter" (tour guide :P), it may not be dirt cheap, but is far from exorbitant.
PS: I've nothing to do with this tour group, don't know about their services and have not met the operators online or offline.