About half of Americans lack any access to intercity transport that isn't a private car.[1]

About 15% of rural Americans aren't within 25 miles of any intercity transit, much less interstate; low-income residents are disproportionally represented in that group. That figure jumps to 25% if you exclude suburbs, and in some states that figure is as high as 62%.[2]

Even as intercity bus demand has increased due to the declining quality of air travel in the US,[3] rural intercity bus access has declined. Greyhound served many rural routes until its slow collapse before being acquired by FlixBus, which is more focused on urban access than Greyhound was. The deregulation of intercity bus access in 1982, which led to the closure of many intercity routes (disproportionally in the rural Midwest) that required subsidization from more profitable routes, was a major factor.[4]

So "what percentage of Americans can't afford a bus ticket to the nearest city in an adjacent state" is a non-starter of a question, because most of the Americans who'd _need_ an interstate bus ticket can't even get to a bus stop without first owning a car... with which they could simply drive to another state.

1: https://itdp.org/2024/01/24/high-cost-transportation-united-...

2: https://www.bts.gov/data-spotlight/85-rural-residents-have-r...

3: https://www.wsj.com/lifestyle/travel/bus-travel-tickets-airl...

4: https://www.thenation.com/article/society/greyhound-bus-tran...