I would not bother too much about the vegitive growing. In Holland we grow with HPS SON-T just one week, then shift to flowering. I know the SON-T is more on the red side, so for flowering, but it doesn't harm the plant so much. Since you are looking at a relatively small space, you may consider using a 600W in stead of a 400W, which gives you a better efficiency. A complete (new) unit would cost around 100 Euro here, which is about 120 $. Second hand would cut cost to half of that.