@CAPTAIN SINBAD can you give some outline to the price differential and if the courses are comparable?
I.e. the $5500 sounds like GUE training, but that would include fundies, Cave 1, and Cave 2. A total of about 2 weeks of training, and goes thru decompression, stage diving, etc.
The $1500 sounds like "normal" training which does not include fundies or most of cave 2.
A better discussion would be to look at the $/day that the instructors are quoting. Solo or buddy class? Does the instructor have to travel, or are they local?
MOST instructors I've seen charge $300/day for solo class, or $200/day/student with a buddy pair.
If we look at Steve Martin, he charges $275/day/diver in Mexico. It includes gas fills *call it $40/day*, and equipment use if you don't have it.
Most Florida cave instructors are $300/day, but fills and equipment are not included. That's not a bad deal.
You need to post some more information on the costs that you're looking at, where they are, if the instructor is travelling, what the course includes, how many days, etc.