.... What's the solution for chains for high millage with out buying shares in a chain manufacturer?
For the hard miles, use an IGH, if you don't want to spend time and effort worrying about chains.
When I was doing a lot of hard miles BITD, I could not make a chain and freewheel last more than about six weeks before it was wrecked. I soon found that a new chain and sprocket for an IGH was required less often and was much cheaper too.
Re chains, the very cheapest derailleur chains from most manufacturers are made in less hard materials, and don't last anywhere near as long. But reasonable chains start at the second rung in the hierarchy.
It turns out that chainrings and derailleur sprockets wear (in a bad way) mainly in response to chains that are worn. So if you find some way of running with a chain that isn't worn for longer, that will prolong the useful working life of all the other bits.
In an ideal world a £30 chain would last x3 longer than a £10 chain, but that does not quite seem to happen.
If you want to get the most out of your transmission parts, a good strategy is to use three or four £10 chains in rotation. Change the chain every week, and clean/relube the chains that are off the bike at intervals, such that you always have a clean chain ready to fit.
You can buy reels of chain in 7/8s; the unspoken assumption is that you will join the chain with a chain tool. In 10s I don't think this is a common option. Even very busy LBSs usually don't bother with reels of chain because they are big, heavy expensive to buy, and something of a faff.
Thing is, a '£10 chain' is about right for 9s , but it will be substantially cheaper than that for 8s, and about half as much again for 10s. 10s chains don't last quite as long as 9s either. In KMC chains an X10-73 is a good value chain, and is about £13 at CRC right now I think.
cheers