Apple Island Resort in South Hero, Vermont has a marina/launch associated with it. I thought it was a pretty decently nice campground when I stayed there, and the staff was quite helpful in general. I didn't check out the boat launch myself since I have no boat to launch (and don't know if they offer an official boat launch service—I would guess not, though of course the buy with beer trick probably would work there as everywhere).
The Arnold Zlotoff antique tool museum on the site is well worth checking out if you happen to be in the area and are interested in that sort of thing. I had no trouble enjoying an hour there (and it's free admission to boot).
