depends how often you use it. if you print a lot, then the cartridge should spec a page count (might be 500 pages). after that, you either buy replacement inks, buy generic refills for cheaper and hope they work, or buy a whole new machine (which some people say is cheaper than buying just the inks).
if you don't print a lot, then the ink dries and the page count goes down the drain. instead of 500 you might get 100 since you need to account for the wasted dried-up ink. and in this case, it might be cheaper for you to print color at your workplace and simply tell your manager / finance person that you'll gladly reimburse the cost of your own printing. might be 20-cents a page, ask them if that's even an option.