First time so please don't shoot me if I get this wrong.
CSI boxsets are currently half price or less in many retailers, it seems that the publishers themselves are doing a "Half Price in October" deal. I've included links to Seasons 1-4 box-sets on Amazon which are only £14 each, £26 less than the RRP!! I can also confirm that Blockbuster are selling the same box sets for £15 instore as I saw them in my local one last night.
The direct link takes you to Amazon with a search for CSI on DVD. There are deals for all 3 of the CSI series,