Co2 question

        Okay I have decided to move my 80 gallon tank into our family room
and with the movement to add CO2.  Now I have a couple questions for those
of you experience in CO2.  What should I estimate as the average cost of a
CO2 sytem that is low maintance?  And again what should I consider that the
aerage cost is going to be to keep rechareging the system?  
        Presently this tank has three florescent bulbs, one cool white and
the other two are GE Grow Lux that I have been cycling for 9 hours a day.  
My intention is to set up the CO2 to turn on when the light turn on and off 
when the lights turn off.  Is this a good idea or not?
        Any onther initial pointers would be apreciated.

        Oh this tank is going to be mainly planted with sword plants of 
various types.  I also have some 3rd and 4th generation Amazon Swords and
will be also adding a crinkled leaf variety of swords and pigmy swords for
the foreground.

Thanks for the help.