How would that work when you may not even know where the person wants service? You might know a general area and there might be unknown fees that the isp cant know until after they negotiate with the various stakeholders to build service.
Generally you'd probably negotiate w/ stakeholders BEFORE advertising. I'm not sure why any sane person would advertise something before having a solid idea of what is possible, unless they are running for political office.
Often the more expensive service is more profitable but if you want simple pricing you can do the opposite.
No cost until the service location is known. It's a two way street, right? It's entirely reasonable that if you were to obligate the ISP to deliver precision in pricing they'd have no recourse but to require accurate disclosure of the service location.
This is all fantasy, however. This clown world we've built doesn't contemplate such things. The minor ask the FCC is making here is as far as it will go, and if the big ISPs put enough campaign money into the right "family foundations" we might not even get that much.