Get a Brother black-and-white printer/scanner combo laser. I have one from ~2016 that still goes like a champ, even over wifi.
If they're really going 30-50 pages a month the toner cartridges will last 8 months, and since it's toner, not ink, it won't dry out. Yes, ~175 for a refurb unit isn't exactly cheap, but it will print for about half or less the cost per page than an inkjet.
If your mother really wants color, see how often she prints photos and such. If it's only a few times per year, suggest she get them printed at a local library or copy shop. My local library does color printing for, IIRC, 10c per page, which is pretty close to cost.