If you shell out on the bigger, bucket size (and it is actually a bucket), they should last you a fair while - I find I use 4 wipes each time (two for each seat) and they only need doing every 4-6months really, for example. Although I did use a few more the first time when they were comparatively quite dirty, they should still last me a good few years which isn't too bad for £24 delivered.
One tip though; use gloves when using them! The new leather scent seems to seep into the the pores of skin and your hands will smell like leather for a week no matter how much you wash them.