do you mean Blue Spring near Orange City (Daytona Beach)?
if so, the cavern/cave is a single shaft leading down, so the concept of "average depth" is not really applicable.
the spring basin is about 10 feet deep, with areas on the edges around 2-3 feet.
once you enter the opening you have various ledges to explore down to about 60 feet.
at 60 feet, it becomes a cavern dive (within the daylight zone) as you cross under the overhead.
max depth is around 120, but max cavern penetration is
100 feet.
you need to be a minimum of cavern certified to carry lights.
they enforce this strictly.