I love the instant ink program. I have been using it for a year. It is really good if you do a lot of colored prints.
I pay 9.99 a month plus tax. So its about 10 dollars. This gives me 300 pages a month . If you do not use all the pages, they carry over to the next month. They will send you ink cartridges when you need them. They really do last. It take 2-3 months before I need new cartridges. You get them before you actually need them. There are smaller plans, depending on what you print. You can also print more pages for a small fee. For my plan you can get 25 extra pages for 1.00.
The printer I have is the HP Envy 7640. I love it. It's a printer-scanner-copier in one. I love this printer. I haven't had any issues since I bought it.
If you use this link below you can get one free month, of service. This would be a great way to try it out.
http://try.hpinstantink.com/hcqV2 (anyone reading this post, can use this link.)
I hope this helps. If you have any questions, let me know.