The cheapest possible base a Physical race can make, with the cheaper variety of C&C comps, comes out to 1650 min, 5200 org, 475 rad. This has maintenance costs of 165/520/47. Add 2 robo farmers, 2 robo miners and 2 robo rad ext. It now costs 5650/5400/1575, with maintenance of 565/540/157. At a 100% value asteroid, it produces 1200/1200/1200, which means it is still fairly profitable.
Now lets look at a ship. Take a Light Frigate, with enough engines to go speed 3. It has 12 fusion engine IIIs and only 6 fusion reactors, so can only go a range of 2700 / (12*16) = 14 sectors before it runs out of supplies. You can certainly tweak its engine / reactor ratio to get longer range, but it makes it take a lot longer to get some mining done, reducing profits. This leaves room for exactly 2 mining components. Robo mineral miners brings the cost to 3780/1970/2685, with maintenance of 1058/551/751. So it costs 2360 resources total in maintenance per turn, and makes at best 2400 resources from 200% value asteroids. Now certainly you can make use of planets with moons, but it is more profitable to colonize them if possible. This is about the cheapest miner you can get with 2 robo miners. Lets look at one with 6 miners at level 3. It is a cruiser with 19 engines and 12 reactors, so 2 movement per turn. Cost is at 10440/4960/5095, with maintenance at 3027/1438/1477. It can make 3200 of each resource per turn at a 200% value asteroid. No minerals profit, really, though decent rads and orgs profit. Clearly, ships are not very good for remote mining with 2 miners per ship. Now lets try 3 per ship. Same cruiser. It can only mine 2 types now, so lets pick 3 min and 3 rad. Cost is now 10940/4760/5345, with maint at 3172/1380/1550. It produces 4800 min and 4800 rad at a 200 value asteroid. Only 2400 min and 2400 rad at a 100 value asteroid. So at best, total resource profits are 3498. With 100 value asteroid, profits are -1302. Mining with ships requires high valued asteroids. Ship mining is still not a good option.
