There is no need to send people to mine asteroids, it is not like they are going to be wielding a pick-axe. The two sample missions we sent to nearby asteroids Bennu and Ryugu found they were "rubble piles" rather than a solid chunk of rock or metal. Just a big pile of rocks loosely held by gravity.

So "mining" consists of sending a robotic probe to an asteroid of this type, slipping a sturdy bag around a suitable sized rock, pulling the drawstring tight, and flying away. The bag is to prevent loose bits from falling off and possibly damaging the probe.

My math shows a 10 ton probe with 26 tons of propellant can haul 1000 tons back from a nearby asteroid. Since some asteroid types have up to 20% carbon compounds and water, which can be turned into more propellant, the mining process can be self-fueling after the first trip.