Buying K-cups from Amazon should probably be one of your last choices because the prices aren't considerably lower than any other place and you can't use any coupons, discounts, etc.
I've had a Keurig B70 of my own for about a year now and my experience has been that getting K-cups for super cheap is dependent on what stores are available to you as well as your taste preferences. If you aren't overly picky, you may be able to find some sale/clearanced K-cups every so often.
Target - I found some on clearance once because they were going to expire in 3-4 mos. Don't know how often you can find this though.
KOHL's - can't speak for variety but I know my Mom has picked some up from here before and I'm sure they were cheaper than what you would normally find them for.
Costco - They have a "decent" deal if you can handle 80 cups of the same coffee. ~$38 for 80 cups = $0.48 each. In my experience though, Costco only carries 1 or 2 kinds/flavors so your choices are very limited.
BB&B - as 1NF suggested, they have those 20% coupons that they give out like candy. Using those coupons, a box of 16 or 18 will run you probably just under $9 before tax so it'll probably cost you about $0.50 a cup and they usually have a wide variety.
What I suggest to you here is to consider your value of "time" vs. cost. If you don't mind the time involved in "making" your own K-cups, I would suggest one of these
bad boys. I use this from time to time in addition to K-cups. The great thing is that you can make virtually anything with it (Tea, Coffee, Hot Cocoa) and use whatever flavor/brand of your choice at a fraction of the cost of a K-cup. The obvious issue is whether or not you want to deal with filling the filter with coffee and then cleaning it after every use. I like having both the disposable and re-usable K-cups because this approach helps me reduce the cost of coffee, but I still have the convenience of the disposable ones when I'm in a rush.
On a side note, one bit of cautionary advice for you: don't let your coffee maker sit around for a
long period of time with the water reservoir filled. As it says in the manual, it will calcify and then make your machine not run (either properly, or at all). I once let it sit for over a month and it took some work to get it to brew again. So I would suggest running a cup of water through every few days or just purging the reservoir when you won't be using it for an extended period of time.
The only thing I can think to try, other than Amazon would be Bed Bath and Beyond. They always have the coupons for either 20% off your order or $5 off of $15 and I saw in their add that they always offer free shipping, so that may be a decent deal.
