Not really easy to do properly on your own. Cerakote should be baked for proper bonding and curing. In our humid tropical environment, the air dry version doesn't last as long.
If you access to a paint booth, compressor, and oven that can be used for curing, you're luckier than most and you can try it on your own. Otherwise, best to go with the pros - either Red Letter or Xring. You're paying them to get it right for you.
Cost all depends on what your want to get coated, how many colors you want to use, and how big that item is.