I will add to this that I have used Emlid Reach RS with Topcon Total station. In this case you could set up your total station and combine laser with gps and work your way under canopy.
Since I wrote this article I just quoted, Emlid has become better integrated with Topcon, so it’s not necessary to use another software (Field Genius, etc).
Of course, this isn’t a “cheap” alternative, but at least there are a lot of savings on the GNSS equipment from Emlid.
