Or more specifically when using google maps.

Does anyone out there have a reasonably accurate figure reflecting how many kb, mb or gb a typical android phone would use per hour to run google maps as an in car navigation device?

The reason I ask is because the new vehicle doesn't have built in sat nav but it does have android auto ® and before rushing out to buy a new dedicated phone ( android auto ® requires 5.0 build and above and my present phone is 4.4 ) I thought I would try to find out how many gb on a prepaid sim I would need to buy to run it.