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Our window cleaner used to distill his own! Apparently there are places you can buy it on tap (like garages). Pet shops also sell it in fairly large amounts. Not sure how expensive it is but I usually get some from the window cleaner to for a record cleaning machine.
I'm not sure about other methods. When I'm cleaning glass after painting etc. I use a window cleaning solution but I'm either on scaffolding or ground level or the piece is on the workshop bench so no need for a long range solution.
I was looking at window brushes and saw a load of mentions online of adding dishwasher rinse aid to the soap mix. Seems cheaper than buying lots of distilled water.