Didn't make the crossing myself, but saw it done...
So me and a couple mates took a motorcycle ride from Banlung out to the border for a laugh. Got out there and decided to sit and have a few beers or more at a place like 1 km down the road. So after a bit we see these two backpackers walking down the road away from the border, in good spirits though a little frustrated. They were looking for a ride to Banlung, but the couple of folks who were willing to do the ride were asking $50...
So I hopped on my motorcycle and decided see what i could find. The cars I found were asking $50 too, and I was asking in Khmer. Except for one. He said he would take the tourists to Banlung for a cup of coffee. He was headed there anyway so no worries.
He told me that all the cars for Banlung left at 10am and there was nothing after.
So the tourists got in the car and headed towards to Banlung. What happened to them enroute I dunno.
Moral of the story, get to the border before 10am. Otherwise you might meet someone like me who will give you to traffickers.