The trick is to seize on when existing infra projects are being done (major roadwork or perhaps replacing water, sewer, or buried power) and throw the conduit and fiber down at the same time, as the incremental cost is trivial. This is referred to as Dig Once policy.

Fiber is cheap. When you dig, install fiber!

https://www.fhwa.dot.gov/policy/otps/policy_brief_dig_once.p...