This right here. I've never worried about the quantity of chalk I'm using, like wonder_er says it's super cheap and plentiful. BUT I do hate having sweaty slippy fingers, that's what climbers care about.

Also, you may want to offer US pricing and shipping if possible. It's a small thing, but as an American the prices in Euros slightly throw me off and present an impediment to purchasing. It's not logical per se, but it helps to see pricing in the local currency if you want to sell to me.