OK here you go ...
The startup cost of Co2 is a little expensive but if done in a thrify manner can save you some money.
Regulator
Not the top of the line but a great starter regulator, comes with Co2 tubing, FREE SHIPPING, bubble counter and solenoid $86.00
http://www.water-testers.com/content...regulator.html
Now you need something to house the co2 gasses (cylinder) I would recommend a 10lb since this is for a 125gal. $80.00
http://www.aquariumplants.com/Alumin..._Tanks_p/t.htm
Now you need a co2 Diffuser. $15.00
http://cgi.ebay.com/S3-CO2-Diffuser-...item3a4c8bae23
Now you have to determine how much Co2 you're getting into your tank and that's where a Drop Checker comes into play, along with calibrated 4dKH solution.
Drop checker - $15
http://cgi.ebay.com/Drop-Checker-Tes...item3a5ad7b341
4dKH Solution - $8.00
http://cgi.ebay.com/4-dKH-Reference-...item35af3c582f
The expensive this is going to be your lighting, since it is 72" it is rather pricey.
You could go with 2 36"
Maybe 2 of these
http://www.aquatraders.com/Odyssea-36in-2x39W-T5-Aquarium-Lighting-p/52122p.htm
Or this one...Just replace the Actinic bulb with a 10,000k
http://cgi.ebay.com/72-T5-HO-Aquari...118?pt=LH_DefaultDomain_0&hash=item3cb4bbb88e
But this is (if I had the money) would be one I'd get.
http://cgi.ebay.com/72-Aquarium-Lig...044?pt=LH_DefaultDomain_0&hash=item2c5a2ec6ec
Hope this helps, if you have any questions don't hesitate to POP IN.
OH yea I almost forgot about refilling. Most welding supplys around me wants you to lease one of their tanks. So you will need to call around to find out if any REFILL YOUR TANK. Now call some fire extinguisher companies in your area, those that specifically REFILL extinguisher. I have one in my area and he ALSO refills co2 cylinders. I have a 5lb bottle and it cost $14.75 to refill it. It last me about 4 months.