eh, kind of depends on your priorities. If we're talking pure isolation then the pick would be the Brazilian rainforest. Most of the uncontacted and isolated tribes in the world are there. the Australian outback would also be pretty quiet I imagine. But as you can guess, neither those options are particularly hospitable places.
A good compromise might be the American West, somewhere like Wyoming, Montana, Nebraska, etc. Low population density, decently arable land, but you can use the highway to travel to town in a few hours if you need something only industrialized civilization can provide. Low cost of living and I imagine the land would be cheap as well.
