Go ahead and buy. If it gets cheaper, you can always cancel it for refund and rebook at the lower rate.
In addition, if you are getting multiple connections, buy it as one person with multiple devices instead of multiple people with 1 device each. For my little 4 day cruise on Freedom in July, it's currently $79.96 ($19.99 x 4 days) for 1 device for one person so 2 devices would be $159.92. If you buy 2 devices for 1 person, its $123.96 ($15.495 per day X 2 days X 2 devices).