Not free, but we found Makro were usually the cheapest on the WetWipes, but you got to wait for them to have them on offer... Which they do about three months or so... We'd try and buy enough to see us through until the next offer came on...
IIRC, the missus said the nappies worked out cheaper at Tesco's/Boots, as again they used to have them on offer... (Though thinking about it, that might have been as he got older and in bigger sizes...)