Grappling is brutally exhausting, no way doing cardio on a treadmill, bike, stair climber will prepare you.
I've seen marathon runners come in and get gassed after a few minutes. Of course, they were newbies and spent their energy, mindlessly.
Maybe it's just me, but if I take some time off, even a few weeks, my cardio goes to shiit.
That said, IMO, the one type of cardio that I think helps in grappling is wind sprints with jogging in between sets, as it most closely simulates what you do in a hard grappling session: a quick burst of energy to improve position (sprint), then a cool down as you try to consolidate the new position (jog).
Oh yeah, the topic of this thread: I'm paying Renzo $189 a month for unlimited classes, but that's abnormally high because of Manhattan rents. I'd say $100 - $125 a month is the average.