Yes, we know about cost of transporting from the Asteroid Belt, but how about bringing from NEAs? Pickings may not be so rich but delivered cost Planet Earth could be very attractive.
My thinking is probably at odds with most of the enthusiasts around here - I think the
less that is done in space the better the economics and when the economics work then growth, including of activities in space, follows. Conversely, if the economics don't work then growth does not follow.
I think doing more subsidised stuff in space without being profitable, because being in space is treated a desirable and high priority end in itself - and expecting the economics to turn positive afterwards - is wishful thinking. I also don't think activities in space can be treated as a separate economy; activities may be made economic by using in situ resources but there has to be a positive return to investors on Earth. Material commodities need to do more than be useful to those engaged in space activities; actual commodities need to reach Earth markets and make a profit or else the uses in space will be no more than upstream eddies in a downhill flow.
These kinds of projects are too remote and too expensive to rely on wishful thinking or "bootstrapping" - the problems need to be well understood and solutions, as part of a sound business plan, need to be in place before starting. I think the delivery from orbit to Earth is where a large part of the transport costs will be - and very likely the largest part of associated space based activity will be preparing and packaging them for that last few hundred km.
Whilst minimising what gets done in space is important for keeping costs down it still has to involve a lot of space based activities; the near Earth parts of an asteroid mining venture would probably require and support people working in space.
More specifically to your question - I think an asteroid with low delta vee requirements to get to Earth should help. Being closer to the sun - with potential for utilising solar energy - should help. I don't know if solar sails will be suited to moving high mass loads but the less fuel needed the better - whether brought along or produced on site.
On the other hand an object being very cold could make mining easier - brittle materials can be shattered into manageable portions without the energy or equipment requirements that sawing, crushing or plasma cutting would require. Or metallic chondrites - with metal as chondrules that can be separated relatively easily - might be preferable to large, solid metal masses.
I don't know what options might yet get developed for refining the constitutuent metals in nickel-iron asteroid materials in space or on-site - currently I would expect grinding to powder, dissolving in acids and chemical precipitants or electrolytics would be parts of such a process. Not well suited to doing in space or on site I think - a lot of consumable materials that would need to be shipped seems likely.
I keep hoping we may develop better refining; e.g. a way to turn mixed materials to ionised plasma and differentially separating the elements with high power magnetic fields - probably the sorts of things that nuclear weapons treaties would find problematic. But I would suppose they would still be very high energy processes with specialised equipment. Send the refinery into an elliptical orbit that takes it close to the sun to periodically get lots of solar energy?
I think we are still a long way from seeing any viable asteroid mining operation but it makes an interesting thought experiment.