You cannot compare a highway and a runway.
A runway is very expensive to build
AC 150/5370-10G - Standards for Specifying Construction of Airports – Document Information
Why do airport runways cost so much to build? Brisbane Airport Corporation reported that a new runway would cost $1.3B and is seven years away.
Building a runway is even more complex than building a major highway/motorway, which has similar demands in terms of the need for an extremely well engineered surface, high levels of quality control in the materials used, and superior drainage. Runways, once constructed, must be capable of being kept in good repair for many years, including periodic removal of accumulated rubber and other foreign matter and at least one or two major resurfacings. However, it also is understood that runways can in effect "wear out" over time, and may require complete removal and replacement with a new multilayered runway in its place.
The most distinguishing characteristic of modern runways, however, is the need for them to accept increasingly heavy aircraft slamming down upon them and taxiing on and off at many points along their length. The Airbus A380 is certificated to take off at a weight of over 1 million pounds. Aircraft weighing well over 100,000 pounds at landing are the norm rather than the exception at major international airports. To handle such incredible loads on a regular basis -- not to mention temperature extremes in many locations that can easily lead to "spalling" (surface erosion) if not accounted for in the materials used -- runways must be built with care and precision.
A notorious instance of lowest-bidder preference (or penny-wise, pound-foolish thinking) some years ago resulted in a fighter base needing virtually an entire runway torn out and replaced when its rebuilt runway started showing serious damage almost immediately upon its re-opening. The winning contractor was later determined to have extensive concrete pouring expertise... unfortunately, said experience was for the most part confined to laying down home patios.