Even in the era of high-speed internet and satellite phones, a Single Side Band (SSB) radio with a Pactor modem is still one of the most affordable ways to exchange emails while at sea. If you have an HAM radio license and can therefore use the WinLink network, after the initial investment for the equipment the running costs are really close to zero.
On the flip side, you have to acquire some familiarity with the world of radios and its jargon. Plus, if you use a Mac as your on-board computer, you will have to face the fact that most of the softwares (like AirMail or RMS Express) are Windows based. Luckily enough there is way to make everything work on a Mac without too much hacking. Here is Kismet Adventures’ step-by-step guide to do e-mails at sea with your Mac, a Pactor modem and an SSB radio.