From the shape it looks like lice. Lice reproduce every 10 days, so treatment should be done at 10 day intervals. Permethrin is affordable. It comes in a garden dust available at most feed stores, and also in a spray bottle. The best value is Martins or Gordons permethrin 10 concentrate that has to be mixed with water in a spray bottle or garden sprayer for treating the coop, roosts, nest boxes, and chickens. An 8 ounce bottle from Tractor Supply is about $10. Mix that one 1 tsp or 5 ml per quart (32 ounces) of water. Here is some reading about lice and mites with pictures: https://the-chicken-chick.com/poultry-lice-and-mites-identification/