Keep in mind too that the internet on the ship is usually priced per minute.

The internet on your phone on the ship is usually priced per Megabyte, and it's probably at 2G speed or maybe 3G. I have had some fairly decent speeds on the ships WiFi or onboard machines

There is also usually a bonus for booking the block of time the first night which also cuts the cost a bit.

Paying per minute unless you are only sending tiny text files is probably going to be much less expensive than paying by size.