Take a look at the mailasail website. It is specifically for long term cruisers. They will give you a patch which blocks all crawlers from uploading data to your computer other than the specific site that you want.
It literally saved me a fortune. Fleet broadband is really dangerously expensive in the wrong hands.
The owner of mailasail is Ed Wildgoose and he is very knowledgable. I also found that changing from windows to safari gave me a much cleaner connection and was generally more efficient, therefore more economical.
If you are running maxsea it will run on safari through bootcamp but the keystrokes become muddled so it is not worth the hassle. Macenc will give you easy navigating and clean downloads on safari with passage weather which was fairly accurate.
I ran a Fleet system from 2007 installed by Pochon in La Rochelle and used it a lot for business, the costs then were 1k to 1500 US $ per month, I only got the costs under control in 2011 after using mailasail. Prior to that my heart was in my mouth everytime I had to switch it on.
Skype, electronic book readers, any apps. on your laptop will automatically search for updates and you have know way of knowing until you disconnect and see that you have a ton of megabytes on your Thrane and Thrane dashboard.
Worst case was trying to download the Furuno radar manual off the coast of Africa, I managed to spend US $ 750 for zip!
former owner Seafever