I think you'll save money. one solution to the multiple covers issue are the one-size covers. adjustable like bumgenius, but they are only a cover. once nice thing about these is that you can adjust the fit pretty well, accommodating for thick legs, skinny legs, whatever http://nickisdiapers.com/catalog.php?category=2236
Not shown at the link above, but I really like the "wonder wraps" - they are a nice material that is waterproof but breathes and doesn't feel plastic-y, and adjustable rise snaps so it grows with your kid (cleans very nicely too). you will have to buy multiple prefold sizes, but you can use the previous size as a doubler when you move up a size. I actually skipped a size and just dealt with adding an extra fold to my prefolds. DS is nearly 20 months and I've only bought two sets of 24 prefold diapers (I bought this current size WAY to big by accident and just made do, and it's been fine). pretty cheap.