Let's be clear. Refilling inkjet cartridges is easy to do, and hugely economical. It used to be said, long ago, that this was bad for the printer, and the printer companies that make most of their money on overpriced cartridges want you to think that. Ain't so. That's a total scam. Hard to believe that we're still being dimwitted about printer cartridge refilling.
I've been refilling ink cartridges for a decade, and maybe a hundred reams of paper. Takes minutes to refill. I do it every three or four of weeks. Now, I should say that I ONLY refill black text ink. I don't use color.
If you want to do this, you MUST buy a printer that uses unchipped cartridges. The chipped cartridges count how many pages you printed, and refuse to print any more after that. I've been using a Canon MP280 for a few years, and I've bought maybe one black ink cartridge for it. Have refilled that cartridge at least 25 times, and it's still going strong.
I've been using a bulk dye ink they call Durafirm. Really not sure who makes it, but you can get it at a number of online retail outlets. On the order of $20 for 250ml, which is good for 40-50 fills. The necessary equipment is ink and a plastic syringe with a wide-bore needle. Real simple. You do have to bore a small hole in the cartridge once, but that's easy to do. Just put a piece of tape over the hole, and then pull the tape for every refill. There are instructions online for all kinds of cartridges.
I use el-cheapo printer paper (~$4/ream) that I get at my local food store. Works fine.