well found this page. for me to run a 400w light 18 hours a day for veg it will cost me $50.00 bucks more a month. same light now on for 12 off 12 on / $20 to$25 bucks a month not to bad . thats in a room by 6H x 4L X 3W
http://www.northernlightswindsor.ca/faq.html#q9
For what it would cost you to buy one of these tents you could build your own 4 x 4 x6 H box. Right now im taking mine down to move. soon as I get to the new place I will post pic of it . cost to build one under $100 bucks.