We had Nipo microchipped at a Humane Society microchipping event and it only cost $5! When we adopted her from the Humane Society microchipping wasn't as mainstream and they hadn't microchipped her before adoption.

I think we had Jack microchipped at the Veterinarians so it probably cost significantly more.

Our Humane Society also microchips all outgoing animals at the same time they are spayed or neutered.