Hi! I am pretty much going through the exact same thing as you, I am switching my 18 month & 3 month old boys. My toddler is a whopping 29 lbs but by baby is only 13lbs and long. The premiums I just ordered are HUGE on the baby, impossible for him to wear. I am also ordering some pocket diapers and all in ones to try. We are on a budget too but I also don't want to order all of these prefolds and find out it's too much too handle or the older one won't have it. My original thought was to do prefolds on the baby & all in ones for the toddler but the prefolds are too big I have to order more. Anyway, I'm also thinking that the one size diapers would be fairly economical, they could share them and I could get less. Sorry, rambling a bit. I have actually been approached to host a cloth diaper demo class at my home in Lakeview. The woman owns Love Bugs, Co. (www.lovebugsco.com) she is extremely helpful. If you are in the area, would you want to attend, or any other moms out there?
Well, I hope I helped a little, I mostly thought it was interesting that we were going through the same thing.
Good Luck! Please email me if you or anyone else reading this is interested in attending a class.
Edit: My understanding is that there are lots of all in one diapers that take just as much drying time as prefolds, just thought I'd throw that in!