I bought my box on Amazon for about 5.99. A little high, but not too bad. There are some prep issues. You'll need a 8" square glass pan. This pan has to be imersed into a water bath. This is a little difficult, but not impossible.
It is a lot less sweet than I expected. It has a fudge, gooey-like consistency. There are several complaints on the Amazon website about it disturbing people's digestive systems. The general warning is to eat it like a treat and have one-inch serving. Don't wolf down an entire box.
I might be hesitant to buy again, experiencing some dietary distress myself. Never fear, I'll be showcasing another brownie mix that will agree with you. (I've already tested it.)