Call or drop by and ask if you can observe a beginning and a more advanced class so you can see where the teacher(s) start and where you will be a few months down the line. Some studios are made up of a group of teachers who teach their own classes and other studios are single owners.
Assume you will need to start in the beginning class. Even if you come from another studio and were in an advanced class. Teachers prioritize dance steps differently than others and you may find that there are steps in the beginner and intermediate classes you haven't learned or haven't used in that way! Ask if you can "test out of lower levels" or if there are auditions that will enable you to move on ahead.
Be aware that there are several styles of belly dance! Check out and see what the differences are if you are new to belly dancing. Grabbing the cheapest class may not work for you and then you feel stuck or worse yet get turned off of belly dancing all together!
The Dreaded Question! for most dance teachers is...Well I took (insert other dance form here) for years. So I want to go right into the advanced class! Is that alright? And the (probably) equally Dreaded Answer! is no. Belly dancers from other forms of belly dance pretty much have to start in the beginner's level of a new belly dance style! I've even been assured that "I hike, run, play tennis....and am in good shape. Can I start in a more advanced class. My answers have been... Would you run a marathon first thing as a new runner? Or...We don't belly dance with backpacks on! Or...If you can't form an isolated horizontal figure 8 how in the world are you going to move with it!?!
So...Belly Dance is a journey not a destination. Have fun, work hard and take pride in your accomplishments!