This is a very sore subject for some people. It sounds like you're at a franchised studio. I started out with a contract for a lot lessons myself, and I wouldn't recommend it. I had good instruction, but it's crazy to take someone who's completely new to dancing, and sign them up for a huge commitment. Fortunately for me, dancing has become a major hobby, so I went thru those lessons quickly, and learned a lot. But, that's not always going to be the case.
Couple things.. the studio is probably trying to sell you on the idea that when you buy a lot of lessons, it gives them plenty of time to teach you technique and not just steps. My answer to that is why can't you start a program where you're going to work on technique, and just pay monthly as you go?
Also, they probably offer a discount per lesson if you buy a big package of lessons. But, what if it turns out you don't like dancing, or you don't like the studio? If you signed a contract, then you're commited to dancing at the studio for a while.
You're the one paying all the money, so you should have some say in the decision. I wouldn't recommend buying more than 10-20 lessons at a time. They should also teach you the same way they would teach a student who bought 50 lessons. If they balk at that, or you get the impression that they're teaching you differntly for not signing a contract, then leave.