Continuos ink systems
Years ago, when I still used home printers I became furious at cartridge prices and small capacity.
I had a continuous ink system installed which came with the ink tanks full, enough to print way, way more than the few millilitres of ink in print cartridges.
A LITRE of ink from the fellow who supplied the continuous ink system cost about half what a single cartridge cost.
Just out of curiosity I tried peeling back the HP cartridge labels and injecting a few millilitres of ink - worked perfectly!