When we started CD it was pretty important for us to keep it cost-effective. We got away with a dozen prefolds and about 4 covers in the beginning. It worked okay, but I'd definitely recommend two dozen prefolds and about 8 covers, just as the previous poster pointed out.
I primarily use GMD prefolds (I got the bleached Chinese) and Thirsties covers. I've got a couple of Bummis Super Brite covers, and they were great covers, but they really haven't held up very well for me (the velcro). I just replaced them with Thirsties (although now I'm wishing I'd tried the Thirsties Duo). I prefer to use Snappis because for some reason I have not mastered the art of the trifold.

Initially we used prefolds and doublers (hemp & cotton) for night time. I just thought it was too bulky, though. I ended up using BumGenius pockets for nighttime and that has been a good solution for us. We were able to get started with just 4 for night time use only and that was pretty cost-effective. I do use the BG and a few FB pockets for out and about use now (I just think they're trimmer under clothing--particularly jeans), so I have added more (almost all of them bought very inexpensively as they were seconds).
Because we were doing this on the cheap I did make all of my own wipes. I just raided the remnant bins at places like Hobby Lobby and Wal-Mart for cheap flannel and cut them up and serged them together. I also used old baby washcloths that I had lying around. I have over 100 wipes and have probably spent less than $5 on them.
For the pail I found a great lidded trash can at Target. I just use that with a pail liner (I only have one...I really would prefer to have two) and it works just fine.
We don't have a diaper sprayer at the moment, we just dump and swish. Personally, I would probably prefer a sprayer, but my husband doesn't think it's necessary. So, out of sheer apathy, we just haven't hooked one up yet.