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There are Inmarsat 4 providers, e.g. Satcom Direct
Aircraft Satellite Communication for Private Aviation, Iridium, Inmarsat, Aircraft Phone that offer packages per aircraft on a fixed fee basis. I can't help with the actual costs at this stage, but will have a dig around.
Update:: 4.8KB data rates would cost less than US$5.00 per MB - depends on the provider and the actual service plan. SATCOM installation is about US$100K per aircraft, but that's a given on most fleets these days.
mm43