Valerie,
Follow your first instinct, 90 feet is too deep for someone that hasn’t been in the ocean before, currents and probably average vis, boat diving is different from quarry diving. I’ll talk to Gary (nitrojunkie) this weekend. He lives in Myrtle and should be able to give some good ideas for some 40-60ft stuff to get you started. He is bringing 5 others from that area, amybe I can arrange a tour!! For a nominal fee ;-)