Subwoofer hitting floor...solution?

My setup is in my basement finished with carpet over cement. My subwoofer at times hits the floor; if I use a flashlight I can see it hit, then it makes a popping sound. It is mostly during movies with DTS HD MSTR and DolbyTrueHD etc. I was thinking about raising it off the floor but cannot find much of anything that would support the sub and keep it from slide around. Maybe putting it on a flat surface like a granite block or maple wood. I found these: http://shop.mapleshadestore.com/prodinfo.asp?number=AS18X15-CL but they are a little out of my price range. These supports I don't think would be safe to put the sub on: http://shop.mapleshadestore.com/prodinfo.asp?number=ISOBLOCK1-ST.

Anyone have any ideas on what could work well and are affordable?