We support you, single-project-need scenario!
Simply sign up for the appropriate Ethnio pricing plan, and then downgrade to free after your project is complete. It takes two seconds to downgrade (more info here) and you retain access to all your data. However, you must remove the ethnio code and change your plan to "free." Only takes few seconds since we hate companies that make it hard to switch off monthly billing. Pure evil, that is. So if you want to leave our code there for future projects, you have to pay monthly. That's sort of the whole point behind monthly pricing, since we incur quite a bit of server costs for every piece of ethnio code that is on outside servers, even when ethnio screeners are all turned off.
Down the road, if you suddenly have another high-traffic project you need to do work for, just upgrade from your Account inside Ethnio, and repeat the same process as above. Ethnio will even inform you how many page views it gets on your account, so you can pick the right pricing plan.