I switched to cloth for DD when she was a year or so older, maybe a little older. I'm trying to remember how many diapers we had. It's been a while.
As she got older (potty-trained at 2.5 years, for perspective's sake) she wasn't needing them changed as often as when she was younger. I'm really drawing a blank here. I do know that I washed diapers 2-3 times week, so I didn't need to have a huge stash of them.
You could always buy 10 or so and then get more as you get adjusted to using them. If I recall, I liked the motherease diapers that snapped, covered with one of their snapping covers (I think that was white). I also had some Fuzzy Bunz that used regular prefolds as inserts, and those worked well for DD. (I think they either really work or don't work at all, depending on your child's build.)
I was able to both buy and sell dipes at eBay, which was nice in keeping the ultimate cost to me lower.