Yup, I use 2" insulation on the top of my full size hives as well. That stuff is not cheap either though.
I use the 1 inch insulation, and put it inside 18X24 ziplock bags to keep the bees from chewing it. IIRC, the 2 inch was twice the price of the 1 inch. I think the 1 inch was $15 a sheet at Lowe's, and I can get 14 pieces out of a 4X8 foot sheet. That's roughly a buck apiece - the 2 inch would be $2 each.
My neighbor tried some of the 5 frame styrofoam nucs this year. Before he bought them, I thought he told me they were going to be about $40 a box...but if they improve survival, they will pay for themselves pretty quick. I think he got 8 or 10 of them, and all still alive so far. He really likes them because it is so easy to feed them - just pour the syrup in.
I just checked the price at the local bee supply place...$31 with holes, and $25 without. I may have to try some this next year.