Round up to 90B, divide by 50 for 1.8B, divide by 62 for average number of counties and that's about 30m per each county, which seems quite excessive. This has the cost of repaving a road at 280k/mile, while Michelin says it costs a million dollars per mile to repave, and 3x that to rebuild the road. I'm willing to guess that most counties have more than 30 miles of road. We also have not discussed bridges and over passes yet.
Sliced again by person, about $264 per human.