As for the first one, the only ones I can easily find are:
https://www.amazon.com/LxTek-Compati.../dp/B0722JFTPP
You'd be looking at HP 950/951 compatible cartridges. Try looking around. That said, probably won't have a lot of luck. Printer makers make most of the money on the ink, not the machines themselves. It sucks, but that's just how the market is, and as long as that's how they make money, they'll try very hard to make sure you won't be able to get them elsewhere.
As for the ethernet troubles: CAT5 and above should all be capable of doing 100mb/s over 100 meters. CAT5e should be able to do 1gb/s at around 20 meters, more if it's good quality. CAT6 can do gigabit at 100 meters, with CAT6a and CAT7 being able to do 10 gigabit at 100 meters. You either have a very low quality cable, or something below CAT5 if your speeds dropped that much.
As for going wireless: Depends how much stuff, how many walls, and what all that stuff is made out of. In my case, I'm about 5-6 meters away, but I have a half-meter concrete wall in between me and the router, so my WiFi speeds are shit, but my ethernet speeds (over a 30 meter CAT6 cable because that's what they had in stock) are fine.