The downside to JLC - any color other than green is a fairly substantial upcharge.
Elecrow (and several other vendors) charge $5 for 10 boards of up to 100mm × 100mm in any of 6 standard colors (green, red, blue, white, yellow or black). Elecrow also allows slots and cutouts and v-scores with no upcharge for multiple copies of the same design on a board.
This allowed me to make 10 boards with 30 of these cable tie supports per board - a total of 300 pieces for $5. As a reminder, v-scores must be a straight line all the way across a board.