At the moment we've just got a single plan with either a monthly or yearly price point, and adding support for more flexible subscription options is high on the todo list to work toward next!
Ah, this answers the question I had about membership models - I was wondering if it has the option to pay per-thing like Patreon does. ($x per Thing posted, with an optional cap of $y, processed at the end of the month.) Works a lot better for what I do than a flat per-month.