These babies may not be the absolute cheapest, but they are the absolute BEST that will last you as long as you need them. They pull about 54-55 cfm @ 1300rpm and are the QUIETEST fans you can get on the market today. Given the legal standing of our interests here on RIU, noise is surely a concern.
The price ranges from $15-$19 CAD @ many online retailers.
You're cfm requirements depend on your grow space ultimately. Find the cubic area of your space and make sure that amount is exchanged every 1-5 times per minute (as a rule of thumb).
Say your area is (LxWxH) 5ftx5ftx5ft = 125 cubic feet. You need a fan with 125 cfm AT LEAST. In this case, you could use a fan with 125-625cfm. But remember, the higher the better ... as with many situations
If your space is 148cf or less these should do you fine IMO. Take into consideration your temperatures as well. In an environment that's too hot, higher cfm fans will help to exchange larger amounts of the hot air. With your 150HPS you shouldn't have too much trouble I hope.