Remember that Crown Copyright is 50 years and has expired on most of the maps that interest us, so if you have originals you can freely scan them and put them on a web site. It is a bit greedy to charge people for what was free.
There are sites other than NLS with a good selection of OS maps too. Can't find the links as I am using the phone right now, not near the PC.
Sadly you can't freely copy material from old - maps because their site makes a new "arrangement" on which they can claim copyright for 70 years. I always feel that that is unfair as they never did the real work of making the maps. But if you or I make a copy from a legally free source we also can claim copyright for 70 years. I hope no-one here is greedy enough to do that without releasing them under a free licence such as Creative Commons or GPL. That effectively makes them free foe ever, so we will never have difficulties finding the maps we need again.
The business model of old - maps is very much last century and if they close down it will be a good thing. Information, including maps, wants to be free in this century and even the Cameron government is taking that view to the extent possible. Strangely, Blair/Brown took the opposite view, possibly due to being cronies of Bill Gates.
Cameron tried to do something about copyright on "orphaned works" but the EU severely constrained what he was able to achieve. Maybe after Brexit...
(Puts flameproof suit on...)
:)