We visited the cave in the late afternoon and didn't expect for any tours to be available to us. Tours are run each hour between 9am and 3pm, this is the basic cave tour. If you are wanting a more specialized tour, these are less often and need to be booked. The tour was $28, which I initially thought was a bit pricey. There were 3 of us on the tour and the young guide was informative, professional and knowledgeable. The cave tour was the most interactive that I have been on, and it took about 1.5 hours, with plenty of discussions amongst us about times past, photo ops, etc. At the end of the tour, I felt I had got my money's worth, and the fact that there were so many scheduled tours, I didn't begrudge the entrance fee.
If you are in the area, well worth a visit.