Beat me to it. If it's "cheap" that means it's effective. Where I train we do plenty of neck cranks and as such, I'm aware of the openings. The crucifix neck crank is another that is occasionally seen.
The most common but least effective IMO is the can opener style neck crank (usually done from inside someone's guard, but if I'm going up against someone who had been trying to rough me up I'll do it while doing a knee ride, its not pleasant)
other than that all I know is the crucifix neck crank, typically done off a pancake or a butterfly guard sweep.
And I had to post this, I've never watched it (very curious though) and since its on topic maybe someone else here has seen it: