You might want to look at structuring your pricing in a similar manner to gym memberships given that the product has a similar usage pattern. There was an interesting Planet Money[1] podcast recently that noted that many gym memberships are structured to be yearly contracts ... because people like that idea of putting money down so that they feel committed. You might be able to tap into some of the same psychology.

1 http://www.npr.org/sections/money/2014/12/17/371463435/episo...