I spent about $130 for my co2 set up, tank, regulator, bubble counter and ceramic diffusor.
$80 for the azoo regulator from fosters and smith. (a lot of people have bad things to say but it works just fine for me. The needle valve on this regulator is hard to adjust but once you do get it just right it stays put. I guess you can upgrade to a better valve if you'd like to constantly adjust and finagle with your co2 but I set it and forget it.
The only issue I had with it was when I tried to split the line. Since you can't really regulate the pressure, it didn't have enough pressure to run 2 lines with inline needle valves, so something to consider.
$4 plastic inline bubble counter
I love this because they don't break, and are clear just like the glass ones. I've broken about 2-3 glass ones and I just gave up and bought a plastic one.
$20 for a glass diffuser from aqmagic.com
and the tank, the tank I did some weird trading for and ended up paying about $20-25 bucks for a 5lb tank. Bought a 20lb for $60, traded it for a 5lb tank w/ regulator, sold the regulator for $35 or $40 (don't remember)
So yeah, buying off the shelf products can be a good way to go. I'm sure you can get higher quality stuff but what I have works just fine.
Edit: I was in the same boat as you. I had no idea what to get when I started out, and all the terms really threw me off. Basically, you'll need a regulator that has a needle valve attached to it (this is to fine tune the rate of flow). A solenoid is needed if you want to turn it on and off at night. I have my set up hooked up to a timer so it turns off when the lights are off.