There is no set amount regarding how much money one can earn. The more quality Hubs you write the better your chances of earning more. Personally I have 50 Hubs and am now just seeing a noticeable increase in my earnings. I have been a member for over two years, and had I been more diligent about submitting articles I'm sure my earnings would be higher yet. It takes time and perseverance as well as quality articles to earn on HubPages, but it can be done.