I love HP's Instant Ink program ($1/month for 15 prints, I fluctuate between the $3/mo for 50 and $5/mo for 100, based on how much I think I'll need-- it's easy to switch back and forth). You're also allowed to rollover some of the prints- so if you pay for 15 a month and only print 8, you don't lose the other 7, they'll roll over for the next month. HP sends new ink cartridges when your printer sends them the message that you're running low & sends you a postage-paid envelope to mail back the used cartridges for recycling.
You need an HP Instant Ink compatible printer, I have the OfficeJet 5525, but there are probably cheaper models with fewer features that work.
I love it because I feel free to print whatever, whenever, haha. If my kids want a map or a coloring sheet, or to print a picture to send to a friend, I just let them. Pre-instant-ink, I was so concerned about "wasting ink" that half the time, the ink was dry when I actually decided to print, LOL...so it was wasted anyway.
When I signed up, it was free for the first 2 months and then I used my mom's referral link & I got a 3rd free month. I signed up with the 300 prints per month package and printed 900 pages for free (which was super handy as I had just started teaching preschool, so printed half-a-year's worth of materials), then I bumped my package down to 50/month
If you decide to do Instant Ink, you can use this link for a free month (and I'd get a free month too) but if you don't want to use the link, it's okay... the great things I've said about it are true whether I get an extra free month or not
http://try.hpinstantink.com/sBnlH