Copy and pasting a relevant comment of mine from a while back. I crunched these numbers for a random county that made the math easy, but it's similar to any rural area.

https://www.fhwa.dot.gov/policy/23cpr/appendixa.cfm

Roads have an unbelievable cost when you really start to put the numbers together. A lane mile of a new interstate on rolling terrain costs 6.2 million in 2025 $. Keep in mind that is only a lane mile, so for 2 lanes in each direction, it's $25 million per mile. Multiply that by the 49k miles of interstate, and you have a (super rough) estimate cost of 1.2 trillion to construct it today. Even resurfacing those roads is ~1/10 the cost, which is still a lot of money.

Ignoring interstates and looking at really run of the mill arterial is still staggering.

Picking a random square farming county, McPherson county, KS is an easy example. It is 30 miles by 30 miles, with a paved arterial every mile (ignoring towns). Thats 3600 lane miles. At $3.6 million per lane mile, that's ~$13 billion to costruct the roads in a county with a population of 30,000, or $432,000 per person.