Best deal is to spend the $50 and get two of the automatic bingo machine things - the big red "digital" ones that look like a 1987 cell phone. It's the only way to play, ya'll, and you might actually win something with those.
The big final jackpot bingo on the final night of your cruise costs more to play, however. So keep that in mind.
AND, pro-tip: If you attend DVC preview sessions, you not only get a free cocktail (or 3 if you say the right things), you should get a freebie yellow bingo punch card for the final game.