I mean, I have a TomTom satnav that has a built-in sim to download latest traffic updates and sync with my TomTom account. The device was about £250 when I got it 5 years ago and there is no subscription to pay at all, it has "lifetime"* always-on connection. So I can't be that expensive, or TomTom would be losing money by now.
*lifetime - defined as "lifetime of the device", whatever that means. 5 years in and it still works fine.
The mfgr must have negotiated something with one of the cellular carriers to give them unlimited access for a fee, with the stipulation that it's only used for these occasional OTA updates which really don't use much data.
However, I must point out that a satnav device's occasional updates, as I said, don't use much data: just a multi-megabyte download every few months at most. But streaming constant surveillance data from a TV to the "mother ship" is going to require far more data than that. Multiply this by an average of 1-3 TVs per household, and this seems like a big load on the cellular system.
*lifetime - defined as "lifetime of the device", whatever that means. 5 years in and it still works fine.