Printer Ink Cartridges

I'm not one to shop very often.  Just don't like it.  Hate going to the store.  So when I do venture into The Wal-mart, The Costco, The Mall, The Grocery Store, I buy a bunch of stuff at one time.  That way I don't have to go back again anytime soon!

So here's my question, why is it that printer ink cartridges COST SO MUCH?  I don't understand at all.  And why oh why are there SO MANY!

I spent over 80 bucks on a three pack, one black and two tri-colors cartridges.  That's almost a tank and a half of gas! :)  Or that's 53 hot dogs at the Costco!!!   Maybe I shouldn't complain too much though.  I'm pretty sure as long as they don't dry out, these should last me about 10 months due to the amount of printing I actually do at home.   How often do you need to change your ink cartridges?