Sounds pretty standard, although not sure about the monthly fee... Both agencies I have been signed with for modelling/talent have a yearly fee for the online profile plus a one off for them to create your comp cards if you don't have them already. They will also charge you commission per job and probably get you to sign a standard contract where you agree to not sign to any other agency at the same time.
Basically if you get jobs it will be worthwhile, if not it will cost you money! Have you spoken to anyone in the industry about whether they think your son will get work? A neutral 3rd party if possible, not someone from the talent agency

hope that help and good luck!
edited to make more sense!
Edited by nuts_nats