I'm going to be building a variation of this project that should cost much less. Rather than using Nema 6-20 plugs, I'll be using 4 square boxes with industrial raised boxes and a standard 20amp receptacle. So for the cost of one Nema plug, I can get 4 boxes, IR covers, and a good quality recep. Because most of us are using e-ballasts, which sense voltage automatically, you don't have to use a specialty 240v receptacle. Since I use one recep for each 600w ballast, there is no issue of overloading. As for the contactor... i'm using a P&B Prd7ag0-120. picked it up for about $19.