I'm not sure Apollo is the best benchmark. The primary goal was to send the astronauts there and bring them back. Just changing the primary goal should result in a huge reduction in the cost per gram. You'd just send a tiny excavation rover and have it fill bins for the return trip. Followup trips might even skip the rover and just use the one already there. There is a huge amount of room for efficiency and cost savings especially if you leave the humans home.

Though, Moon rocks are a bit of an outlier. They don't have much value outside of science and as a curiosity. You might want to focus on something with more predictable demand. In which case, it may get more complicated than "shovel stuff into a bin".

The $50,800/gram figure seems to be based on the total cost of the entire Apollo project - $50,800 * 382 kilograms of material returned = $19,405,600,000, which is about 4/5 of the total Apollo programme cost listed on Wikipedia.

That seems a little unrealistic to me, because the goal of Apollo was not "bring 382 kilograms of moon rocks back at the lowest possible cost", or anything close to it.

Obviously there are some big hurdles to overcome, but I don't think they're as enormous as "reduce cost by a factor of well over 1,000".

Don't Musk's reusable rockets bring down costs by 80-90% if I recall correctly he and the Google founders also own a space mining company. Space mining might come faster than people realize.