* Make some new larger plans, with some enticement to convince current subscribers to switch. "Normally $60 a month, but only $40 a month if you sign up now..."
* Offer quarterly/yearly billing. Let people lock in the current rate if they preorder, or even offer a small discount in order to get the cashflow bump.
* Overall, don't get into the situation where $5 makes or breaks profitability. If you are indeed helping e-commerce merchants process orders with nontrivially less pain, $30 or even $90 a month is nothing to them.