costs around $10 per MB (and believe me you burn that quickly) and Inmarsat rather less but set up costs a lot more. Speeds are, with a very expensive set up (sub superyacht), comparable to dial up speeds of 15 to 20 years ago or rather slower.
But, as ka4wja queries… why would you really want to? Part of the joy of being in the So Pac is that you have almost no comms. No planes passing overhead, and precious few even visible satellites. Wonderful!
But if that's not your juice then ozskipper has the best and most correct solution.
Other than that, for grib files you can use saildocs with SSB
or else Iridium phone
for not much money
using mail compression
services etc. Those are useful and worthwhile.
It is REALLY worth downloading as many satellite images
of intended island groups and detail of those islands/atolls prior to departure with a mainland connection. It will be worth the time and effort, believe me, as satellite
imagery is your best bet for accuracy in the So Pac.