I have a customer that wants her driveway enlarged about 1.5ft on either side. She wants cobblestones dug in, level with the driveway. The driveway measures 37 feet on each side. What kind of a base should I use, there won't be constant car traffic on it, but sometimes there will so I obviously don't want them to sink. I have never done something like this before, looking for some hints on the base needed, and any other tips, thanks! Even pricing help?