For a ~$10 billion constellation with an individual satellite lifespan of 5 years, the system would need to average ~$170 million per month for something resembling break-even. Current US satellite internet adoption is at 6.7% percent; push that up to 10% so I have some number to work with when accounting for market penetration and the rest of the world, and you’re looking at 32.5 million users, which sets an absolute price floor of $5.25 a month. Give it margins that actually make this remotely profitable and $20 a month for service wouldn't be unrealistic; the upfront costs of the uplink would probably still kill you though.

Edit: Did some more research on competitors. It seems ViaSat currently has 1.1 billion invested in its 2 active GEOs, plus whatever’s currently going in their next generation constellation. Their bargain bin plan goes for $70 a month (fun fact, they too pull the 3 month deal BS landline ISPs do) up to $200 a month. Since it only has a single real competitor it probably services 3% of the US population, so with their midplan of $150 a month over 9.75 million users into a satellite constellation with a lifespan of 8 years they are charging in the neighborhood of %12,700 over their satellite breakeven (1.46 billion month revenue over 11.46 million per month payback).

Bringing that over to a $10 billion constellation with much more premium internet, yikes.