250w cost more then 400w, and 600w cost more then 1000w. b/c then are odd. you can also get switchable ballest so you can run both mh and hps. i would go 400w b/c you will outgrow 250w. allmost everybody outgrows there lights like said above. i started with one 400w then got two then got one 1000w a now im up to four 1000w switchable ballest.