After checking with our utility department, the cost was close to $10,000 for the demo unit we bought. The brand is MALA. He did also state that if you are a member of a utility association(ours being a Florida association), they might have equipment they loan to members. So, prior to purchasing our own unit, for the $100 annual membership fee, we could borrow their cart when needed. We just got to the point where we were keeping the loaner unit for months on end and ended up just buying our own cart. But, since getting the cart, it has saved us several thousands of dollars just on the golf courses alone.
The website for the system we bought is
http://www.malags.com/Home. Ours is the ProEX with the rough terrain cart.
I would try Googling "Ground Penetrating Radar Rental" and see if you can find something nearby. You might find something like this
http://www.malags.com/Products/ground-penetrating-radar-equipment-rental.