Did the 600 also include transfers to and from airport (or next island)?
It covered the boat ride from Belize city to Long Caye. (This is also their supply run.) it did not include the taxi to and from the airport, at $25 usd one way. One more tip, on that. The princess Ramada arranges transfers for $10 to the airport.
If you factor in the cost of other dive trips from San Pedro to Blue Hole, the transport part of that costs around $150 per person, so the boat ride is around a $300 value for a couple.