Are you only looking at Iridium plans? I looked into Globalstar recently, and it was $480 for 480 minutes, good for 12 months. That plan made sense for me, where most of my usage would be concentrated, rather than spread evenly every month.
Text is great, especially for positively communicating things like coordinates to send the helicopter to, but it doesn't replace voice, IMO. Talking to a rescuer or doctor on the phone is a lot different than sending texts back and forth, and it's definitely nicer to hear to be able to hear your kid's voice than get a text from him!
I get it, though, at 4x the cost of text only, it makes it a tougher decision.