http://www.state.ma.us/dfwele/pab/pab_toc.htm#PABsites
I found this in a prior post by doing a search on *ramp*.
If your going south to go to get to Plymouth, try Green Harbor in Marshfield (It's $5 too, but theres docks to make launching an easy one man job).
If your coming north the Ramp by Mass Maritime is good ($5 with dock)
Just over the bridge in Sandwich there is a ramp just inside the eastern side of the canal. (I've never been to this one)
Plymouth has a nice ramp, but at dead low its a slippery mess and to charge $5 and have no dock is just wrong.
Good luck!!!