We stayed at the Sabadee GH for $20. The rooms were OK with good parking for the bikes, but the rooms were loaded with mosquitoes for some reason.
Why are you going to Pak Beng? Unless you really enjoy the boat ride there is no reason not to take the road to Huay Xai anymore. Quite a few riders have done the trip in the last few weeks riding everything from XR250 to a Ducati. Check the reports if you haven't read them already.