And for the Pixel models it also costs $500 per device unless you want to run your own build server.

Do they not provide fastboot images for the Pixel devices? I know I could just flash those images on a Nexus 5X.

For Pixels they only provide images to paying customers. They were mad about people resellling flashed devices because it violated their noncommercial license and even disabled the update servers for Nexus devices entirely for a while.