Can you describe the fly like things? The most common are fungus gnats and they usually are seen on the top of the soil or in that area. Do a search for fungus gnats on here and see what you find.

Giving ur plants a week or so under the new light is a good idea, if they are too stressed when you start flowering the yield and quality could be greatly diminished.

Cheapest/most effective is really in the eye of the beholder. I know if I invest $400 in an HID it will repay me with $2000 of meds I don't have to buy. Seems pretty cheap to me :thumbsup: CFL will work fine, although it isn't the most effective, but it is the cheapest. You can probably purchase a good amount of CFL lighting for 20 bucks or so. Put some pics up after you get this thing going, we will all be watching.