Kitty:
There is a back road, but it is private. They didn't used to lock it when I was a kid, and we used the back road all the time, but it is frequently locked these days.
I don't have any details for you on the extra expenses involved in living in BVS, but in town, it is known for being where the "rich" people live. It ain't cheap. I can tell you that for sure. Here's a website for you...
Bear Valley Springs , and here's the link to the BVS Association
Bear Valley Springs Association - Bear Valley Springs - Paradise Found
I would recommend looking in Old Town... It's close to town, and not so expensive. Plus, lots of places with the other things you're looking for: trees, solitude, some space of your own. In fact... A home near my folks' place was for sale not too long ago, but it's a 2BR/2BA so they were having a hard time selling it. The area my parents live in is in 2 to 5 acre lots, tons of Blue Oak trees, solitude. Let me check to see if that house is still for sale. They don't have a home owners' association or anything like that, but their roads are private, and everyone in the area chips-in when they need to be repaired.