I used dylon on a little lamb cotton terry nappy and it took great but not sure if you want more natural dyes.
As for shapednappies I do recommend the tots bots but Ihave heard others rave about little lambs, though I persoally found them a bit small for Seren. TBH most nappies are the same price between 6-10 pounds, have you looked at ebay for deals?
Perhaps the WAHM's might have better prices,though I don't think they do sets.I amPMing you the address of a nappy site, hope this is ok.