The cost is now $12 per night at Four Mile Lake and it is almost empty if you go during the week. I stayed on Monday July 23 and there were only 4 occupied sites of the 14 to the left as you enter the campground. The campground host said this pretty standard for mid week
In 2013 the trailhead is fee area. It is $5, and there is a drop box in the parking area to pay. There is also a very good graphic at the trailhead to show the trail, as it is tricky to follow above the treeline.