I'm visiting my parents right now. They have what I would term as "rural internet options": satellite, fixed cellular, or dialup. There is no DSL. There is no cable. There is no wifi. Satellite has awful latency and an effective 20GB monthly cap (their advertising is very deceptive because they pool midnight off-peak data in their advertised caps), fixed cellular has a 30GB cap: there is no provision to buy more data on either service short of ruinous overage fees.
Browsing around on the modern web filled with autoplay videos, huge JS libraries, giant pictures, etc. has been sufficient for a 2 person household to blow through that 30GB cap in less than a month. It was hard for me to believe, until I instrumented their network and saw for myself. Of course, accidentally updating any software, accidentally syncing their photo libraries, etc. are all expensive mistakes.
Most effective changes I have been able to make so far (without frustrating the parents too much) have been to ad block and get them to use Opera with Turbo, which has been sufficient to cut their data use by about half. I also put a timer on the cellular hub power supply to manually shut it off when they're not at home or when they're sleeping, because despite best efforts some software still automatically updates.