I tried something similar... Our CEO set the price of our email service too low (oops). But unlike you we faced the music and doubled the price only a year after. The backlash was much smaller than I anticipated. We marketed the price hike by adding some requested features and made the payment term half as long so the price seemed to be the same. This made it easier for our customers to swallow. Of course we lost customers, but not enough to make a difference (about 5%).