Few items in this world are as pricey as printer ink. You can easily spend £13 or more for a small cartridge of colored liquid, whose chemical content and actual cost are closely guarded secrets.
There are other options, but they can be scary, as we found when we tried several options in our real-world “Portrait of a Serial Refiller” series a few years back. 
Companies like HP and Brother run a very profitable business selling their printers, sometimes at a loss, just so you can buy the ink they sell for them. It’s in these companies’ interests to discourage you from trying a third-party alternative. They design their printers and cartridges to make using third-party ink (which is sometimes made by refilling old cartridges) an uncomfortable experience.
That’s why you can get annoyances such as the (otherwise harmless) warnings described by Norm. Another common problem: With third-party cartridges, you may not be warned about low ink until your printer stops printing a particular color.
What’s more, some third-party ink isn’t well made. I’ve yet to hear of a case where ink actually ruined a printer, but I have read about it ruining a carpet. And I’ve read a lot about leaking or empty cartridges, as well as inks prone to smudging.
So if you’re going to try third-party ink, buy from a company with a good reputation (read user reviews), and be aware of the risks. Most likely, you’ll have some annoyances, but no disasters.
Some inkjets are surprisingly affordable
To be fair, inkjet printers aren't the guaranteed money pit they used to be. We've done the math, and small-office inkjets available now are faster and cheaper to operate than comparable color laser models. Many consumer inkjets are also affordable. You just need to do your homework on the ink costs before you buy.
Why not go for a plain and simple monochrome laser printer? You could, but the lowest-cost laser printers are slower and no cheaper to operate than comparable inkjets. You could, however, use the laser for basic prints and use the inkjet only for projects where color is required.
