In desperation I have bought the blue sheets and stripped off the silver vapor barrier. Depending on where you are, you can get the pink sheets in 1/2", 1", and 2" thicknesses--i.e., the colder the climate, the more choice you'll usually have.
And Home Depot may not have the best price by far. Go to the Yellow Pages (or Internet) and look for a local insulation dealer. You might save 50% which, given the skyrocketing prices of the stuff, could be a lot. I bought 10 4 x 8 sheets (in 2002) at 60% off Home Depot prices, and it was delivered free.