I am building in 15 feet wide and 8 foot tall built in shelves in 3 sections. I am looking for the best lighting solutions for these shelves? Ideally I would like to operate with normal light switch I will mount in the shelves, but I am having trouble finding direct wire options. They all seem to be plug in options with built in custom switches or remotes which I want to avoid.

It looks like I could wire in something like this, but with 18 shelves Id be looking at $900 in lighting, and these may be too bright. The pre-built solutions seem much more affordable. https://www.amazon.com/dp/B0CP4J3NBS?ref=emc_p_m_5_i_atc&th=1

This seems designed for what I need, but I am real wary of the touch sensor, and ideally I don't want 3 separate switches.

I used cut to length LED strips (from either Home Depot or Lowe's) stuck to the underside of the top shelf face frame. I drilled a single hole up to the attic and wired an outlet that the lights plug into. I had an available existing switch from before the ceiling fans were changed out to single switch/remote so it was a lot easier than if you have to fish your own switch into the wall

The LED strip is 1000 ways adjustable, but I set it for soft white and now just operate off the wall switch

Edit to clarify: the wall switch powers on/off the outlet I wired in the attic. My book shelves are 5 sections of 40" linear, so I had to go with a pretty robust LED strip per barnacle's note below. It was still only about $90

100% cut to length as stated. I would pay extra for quality strips and power supply. You aren't finding any direct wire options because they need to step down to 12 or 24v.

That is a big area you are trying to light up. There are max length runs you will need to calculate.

I use flexfire for strips and meanwell power supply, but there are a lot of suppliers out there.