I assume there is also some incidental lighting in the caverns. Does that extend to lighting the points of interest you want to point out, or do you need the hand light to illuminate them as well as point them out? If they are illuminated themselves, would a laser pointer be sufficient to attract the viewers' attention, or is more illumination needed to fully bring out the features? And what distances are we talking about here? One meter, five meters, ten or more meters? The further away, the more power the flashlight must have. Plus you will want the light to have enough capacity to last the entire tour, with a little left over as a margin. I can't see a $15 light as being able to do this.
To keep the beam from spreading with distance, you are probably going to need some sort of aspheric lens rather than a reflector light. I don't have any experience with those, so am not going to recommend anything.
Do your guides also carry a backup light or two? A power failure or a dropped light that breaks could be a problem without backup lights.