I linked the Finacard softcard bale on another thread
You need a lot to start with but after that you shouldn't need very much that often as most of it will stay clean and dry and just need spot cleaning occasionally - you can do that for a very long time. If the base needs a wipe at some time and you remove the substrate for that reason you should be able to replace at least half to 2/3 of it again and mix in a bit of new. Basically the more you have in to start, the less you use long term, so it would be good to start with a big bale and see how much is left.