He likely spent a few hundred dollars on the sign - sourcing the proper metal of that size, the reflectors, the masks, and so on.

As to the time investment:

> He spent more than three months preparing, researching the color and shape of the signs, mixing his own custom paint to get the colors just right, and applying a bit of faux patina to finish it off. Ankrom even spent time tracking down the button-shaped reflectors used on other legitimate signs and convincing the supplier to give him some. Once he was satisfied that it looked authentic, he came up with a plan to install it.

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Caltrans has 15,000 miles of state highways that they have signage for. A single sign may only get reviewed once a decade because of that.

Doing single things in isolation is "easy" without going through the required public comments and such. Maintaining it for the entire state is much more challenging.

Caltrans is so frustrating how they do signage and freeway identification. N-S roads sometimes become referred to as E-W roads in signage sometimes simultaneously. Hardly ever showing exit numbers. Actually using the freeways formal longform name in signage. Outside of signs theres also the all too frequently seen deadly combo of zero left shoulder + lowest cement divider you’ve ever seen + modern headlights dazzling you in the opposite lane.