It costs me nothing so far (negligible api costs covered by a grant) and I don't spend anything on marketing. I currently get all my customers from SEO (Google landing page) and the chrome web store. I am currently averaging around 70 installs a day. Churn is 18%. I currently want to sell because I feel like it doesn't really add too much value to the world (helps people cheat lol) and I want to put money into a new venture of mine that adds more value (ed tech chrome extension)