I've read pieces in WSJ/NYT about super-cheap chinese-run busses; a quick Google came up with this -
http://www.staticleap.com/chinatownbus/
The articles rated them above Grayhound, and much cheaper.
Personally, I'd probably go with Amtrak if I couldn't find a low *A fare.
OTOH, sounds like an opportunity for an MR, either as an open jaw BOS-XXX-NYC or a convoluted routing on BOS-NYC.