"It would be cool for so many reasons to have a refuelling base on the Moon, but I think NEOs provide the best bet for easily accessible volatiles. And some are on convenient orbits to be way-stations between Earth and Mars - Earth-Mars cyclers with insitu materials for construction/refuelling."

If there is a large market for rocket fuel, I see NEOs as cheapest source of water/volatiles. Or if there is demand for a billion tonnes of iron per year in Earth orbit or Earth surface, I think NEOs will be cheapest source. I think NEOs will so cheap that water will imported to Earth from them. But all this is pretty far in the future.
The question to me is how do you start any market in Space, and what is cheapest way to get the least amount. In other words, for example your total budget/investment capital is 4 billion. What is the least amount of time to turn that 4 billion into 8 billion dollars and you want to do this in about 7 years.

One of the most critical places to have rocket fuel is in LEO, but another place is high earth orbit, L-1, and/or Lunar orbit.
LEO is critical because it is halfway to anywhere and is the least delta-v from Earth surface. But if you going to high earth orbit and beyond, going first to LEO is not necessarily the most efficient route [compared to directly going to an earth escape trajectory]. And another factor is in the inclination of the orbit. If "everyone" launched from say 28 inclination or an equator launch then that would different situation than what we current "have".
The difference between a 28 inclination and zero inclination Low earth orbit in term of delta-v is enormous- a escape trajectory, L-1, lunar trajectory is closer in terms of delta-v, than changing from 28 to Zero or Zero to 28. So, large changes of inclination at LEO are practically/literally worlds apart.
Changing inclinations and/or moving to GEO, and L's, lunar orbits, from high Earth orbit doesn't require much delta-v, and the most common and nearest in terms of time and delta-v to all high Earth orbits and escape to Mars or wherever, is Earth/Moon L-1. Earth/Moon L-1 is THE international and interplanetary hub.
So that why I say LEO and high earth orbits [it doesn't much matter where but Earth/Moon L-1 or L-2 are slightly better {because going towards the Moon for a gravity assist most of the time would be first part of leg of the trajectory "elsewhere" {{somewhere else in High earth, earth, LEO, or earth escape}}] are critical places for rocket fuel.

In the very near term, the cheapest place to get water to LEO or L-1 is from Earth. If one is dealing with small quantities, and/or not concerned with storing propellent for any length of time- say more than a month, then instead of water, rocket fuel made on Earth will be the cheapest way of doing it. When the quantity is 100 tons or more, but less than thousand tons, water begins to be cheaper, but it's still less to ship water or rocket fuel to LEO or L-1 from Earth than from anywhere else:
100 tonnes equals 220,000 lb if LEO cost 2000 per lb and L-1 cost $8000 per lb: LEO is 444 million and L-1 is 1.76 billion. And obviously 10 times this is LEO: 4.4 billion and L-1: 17.6 billion.

From the Moon, Mars, NEOs it is cheaper to ship water to L-1 than compared to LEO. From Earth it is cheaper to ship water to LEO than L-1. It's about at least twice the price to ship to L-1.
When one is dealing with 1000 tons of rocket fuel needed within 10 ten years, I would say it is still cheaper to ship water from Earth to LEO than from anywhere else. But in regard to L-1, mining water from the Moon could a cheaper way of buying those 1000 tonnes.
Said differently, 20 year from now, the cheapest source of water to LEO is probably going to be from Earth, but within 20 years the cheapest source of water for L-1 could be the Moon. If this is true, than probably the cheapest source of water to L-1 in 30 years will be NEOs and in 30 years the cheapest source water in LEO will be from NEOs. And in 25 years L-1 water could cheaper than LEO water, so NEO water might first be sold to LEO.

If you sent 100 tons to LEO, and 100 tons to L-1 and had a gas station convert the water and sell rocket fuel. You could go from earth surface, refill rocket fuel at LEO, travel to L-1 and refill and land on surface. You could consume those 100 tons in both LEO and L-1 delivering material and personnel needed to establish lunar mining, and power capability to process water into rocket fuel. You could then ferry water and/or rocket fuel from the Moon to L-1. And you could ship more water from Earth to LEO.

With a gas station in LEO, L-1, lunar surface, it would be possible to have reusable crew vehicle capable of withstanding a 5 km delta-v earth re-entry, which is launched from Earth, goes to the Moon and returns and lands back on the earth- something like this probably wouldn't be a winged vehicle, and the capability of low speed re-entry couldn't add much weight to vehicle for it to be practical- but it's conceivable that vehicle built for suborbital travel could go to the Moon and back.
So, if a couple dozen of these are being made per year and were selling for 20 million a pop and with a first stage it could get to orbit, then it's then it's 5 fillup before it's back on Earth- so it's cost vehicle that could go to the Moon say 50 times, plus a first stage rocket every trip plus the rocket fuel costs.
So, around 60 million in rocket fuel costs, say 10 million for first stage and with say 4 passengers. One could have round trip ticket to the lunar surface for $25-30 million.
So, you could go to the moon for about the cost of the Apollo LEM.