A cheap and quick-drying option is terries or muslins folded into a pad and held in place with a Nature Babies popper wrap. Never had any leaks (though you do get poo on the wrap from time to time), and they're pretty non-removable for even the fiddliest fingered child.
I used terries nappies on lo to begin with but once he was at the age of crawling etc. changed over to tots as it was quicker to put on for him, use the velco type as he doesnt stay still for the nippa or pin version.
Good luck Alibubbles - I can't wait to see how it goes - how do you Mums feel about it?
Are they keen? or a bit unsure?
How much will it cost in washing (never mind initial costs)?
I really like the idea btw - it's been in the back of the mind for ages