It costs nothing- I used to install sidewalks among other things, and when installing as new I charged exactly nothing for building an access ramp.
I am sorry it is different in Californica, but that's not my problem.
BTW, A replacement pad w/ access ramps in two directions, removal + replacement was $2500.
Maybe that's why you "used" to install sidewalks.
Every General and Concrete contractor I ever dealt with on the design or inspection end of construction have always charged extra for ramps. Even from scratch.
as for what I addressed originally, replacing perfectly good curb, gutter and sidewalk. My post stands.