You don't need orbital habitats to make AMs work. You just need to not put engines on your mining platforms. 100kt-200kt commercial shipyards arn't that expensive, and they have other very useful applications (like divisional transports, fuel harvester platforms or superfreighters.)
Asteroid miners are particularly useful in the early game. But building tugs is a PITA. So I just stick tractors on various designs that tend to have powerful engines and sometimes idle about uselessly, such as colony ships and troop transports.
In my current game, though, I've discovered virtually no worthwhile asteroids near Sol and the comets all sucked. It's something like 40 billion km to the nearest worthwhile rock field. Urk.
