Thinking about the show, it could truly be done with very little set. Cinderella's house could be a a table and a set of chairs with a stool over on the other side of the stage for her "corner." The ballroom needs no set at all, except maybe two chairs for thrones for the King and Queen. As for the coach, it could be done with just a bench on wheels - granted, the audience is expecting a little bit more, so maybe you could have a giant circle to represent the coach, or maybe since the focus would be less on the house, ballroom, etc. you could have your set crew mainly work on a coach.
Do you have stairs leading from the stage to the house in your auditorium? If you don't, consider constructing some and having Cinderella run down them and down the aisle when she's fleeing the ball. When my dad directed this at a private school years ago (I must have been 4 or 5 and I'm nearly 17 now), that's how he did it.
Really, hardly any set is actually needed
for this show. If you want to go for a simplistic design, I would say focus attention on your coach, because that's what's expected. Also, even if you don't have the stairs going out into the audience, you'll probably want a staircase of some sort for Cinderella to lose her slipper on (even if it's just three or four steps going offstage).
Don't let set stop you from doing this show, because it's perfectly capable of being done without it.