I have an Epson Workforce and I buy all my ink at Staples.
I use the black and color package that is a little more expensive and last longer. I use my priinter daily a LOT and I hardly ever have to replace the cartridges. My daughter does a lot of school projects in color, etc.
Yes, they are expensive.. no kidding there. I usually buy 2 sets at once and always have a spare on hand for the late night projects, just in case.
Sometimes Staples has a special deal. I do take my empty cartridges back and I get credit. I get a check from them about once every 2-3 months for up to $20.
I know there are some off brands out there as well as refill it yourself deals, but I am not willing to go that route. I run my company from home and use this printer a lot and I won't waiver on quality to save a few bucks.