Suggestion for finding a cheap CO2 tank: I found that in my area it was cheaper to get a CO2 tank from a beer/soda distributor than a welding supply co. Re-fills are cheaper there too. Call your local bar/tavern and ask who services their soda guns and taps, then call them up. I paid $50 less doing it that way for my tank. My 20# tank was $125 (already filled), and will probably last me a year, or so I've heard. (The 10# was $100 and the 5# $75.)
As for a regulator and the rest of the "gear" you need, you can look at Rex's site for his products, which are great quality from what I understand.
I didn't want to spend that much, so I went for a commercially produced setup and bought the Red Sea CO2 Pro system from Big Al's. It was $189 with a solenoid. (solenoid is used if you want to automate your CO2 system instead of manually turning it on in the morning and off at night - I'm lazy and thought it was worth the extra $50) I've been very happy with my setup so far, and it came with everything you need to run CO2 except the tank. Also very easy to set up, and I am not a technical person at ALL. It even has a drop checker included with it, however you will need to purchase (BlackSunshine on this forum sells it) or make your own 4dKh solution to put in it, the solution that comes with it is just bromethymol blue and is not an accurate indicator of your CO2 levels.