I have used the Novak Lipo cut off, it works pretty good. You wire on end the battery terminal, esc plugs into it and you plug the cut off into receiver.

When you hit low voltage.. You'll notice motor will cut off and on signalling you've reached low voltage.

Entry level esc's with Lipo cut off are around $100... These are brushless... I assume that's what you're looking for. Keep your eyes on the for sale section, I picked up a used novak havoc for $50... the novak lipo cutt off is $20 to $25!