Haha, do not worry, we have consider this when we design this little cute.
droPrinter use the standard thermal paper, it could buy from any office store and super market, like Walmart.
and you also could buy it from amazon, we have post the screen shot of 3 roll of thermal paper just cost 3.5 USD on amazon. You could check it in the introduction.
One more thing, one roll of paper could be used for a really long time if you do not use it in your business. I means, if you use droPrinter to print invoice, it really could, but this would also "killing paper". ( you may need to change the paper roll every days if your business is very good)