Well if youre from the UK, Id go and buy the 600w CFL that Ive put up in the link above, its been reduced from £25 to £20 so its a decent price.
Plus, I think 600w should be enough to grow 2 plants, but Im not sure. 120w should be enough if they arent the standard lights like the ones in your living room, but you wont get a very good yield (aim for 400w or more for a decent yield). Alternatively, buy a 1000w CFL if you can afford it.