Wi-Fi Rail is going to cover the whole $20 million cost, and recover it with user fees and advertising (I don't know if this means that you will have to pay to use it and still see ads, or if there will be a choice between paying to use it or getting ads.
A few years ago, CalTrain looked into onboard WiFi but dropped the idea because it was going to cost too much (to them). I don't think offers of free installation were forthcoming at that point. Perhaps they should contact the WiFi Rail people.
It would also be nice to see different transit agencies joining up to negotiate these things jointly (there are lots of things like ad contracts, cleaning, power, where negotiating as a group could probably get everybody a better deal).