Need to insulate

I need to get insulation added to our attic. When we bought the house, I intended to tackle this in year 2, but the events in my family last year scuttled those plans. And you don't really think about that kind of thing until it gets cold. So, THIS year I need to do it. I remember that the insulation up there is about 6" deep. But they recommend a depth of around 15" to get the place up to spec. So, sometime I'll be off to the store to get many rolls of the pink stuff. It looks like according to the many insulation websites available, it'll take about 17 rolls to do it. And around $500 for the whole thing. Plus, the Man is still offering tax credits for home improvement work designed to improve energy efficency. So, time to get cracking.