I've started doing some research on those types of things too, as my aquariums need some serious lighting modifications.
So far, it seems like parts progress like this:
(1) plug that goes into wall outlet is connected to the ballast by some length of cord
(2) ballast is connected to the bulb socket by some other length of cord
-- this is assuming a "remote" ballast, as opposed to "non-remote" ballasts that are right next to the bulb assembly.
-- also, ballasts can either be magnetic or electronic (I think electronic is more efficient, but not sure)
(3) bulb socket is what the bulb is inserted into
-- the wattage of the bulb has to be compatible with the power provided by the ballast
(4) all of these items are collectively considered a "fixture"
I hope my explanation didn't seem too simplified, it's just that I find it easier to understand things when I start from the beginning parts (plug) to the final parts (bulb) - so that is how I explained it.
I'm confident that if I misspoke or omitted anything, then others will provide the appropriate info.
As far as prices...I'm not sure of anywhere to get that much wattage for less than $150.
25g Marineland Eclipse (30w T-8 ):
- java ferns, anacharis, corkscrew vals, giant hygros, marimo balls, java moss
- zebra danios (5), otos (2), others TBD
6g Marineland Eclipse (8w T-5):
- anacharis, asian ambulia, java moss
- white cloud mountain minnows (10 = 6-7 inches total)