ferts don't have to be expensive.
For the most part, the usual fertilizers, (phospate, potassium, and nitrate) are all cheaply bought. You can find things like potassium nitrate on the internet for almost nothing, especially when you compare it to the cost of "aquarium fertilizers." Your trace fertilizers may need to be purchased from a LFS though.
This is an article on using these and where you can buy them.
http://www.fishforums.net/Jamescand39s- ... 04737.html
CO2 can also be set up pretty cheaply with a do-it-yourself yeast system. I not sure the DIY systems work all that well on large tanks though. It just becomes cumbersome with 4+ 2 liter bottles.
It is a decent amount of extra "work" though, and you need to have good lighting for the dosing to really do anything. It seems pretty common for the stock tank lights to put out pretty low light ~1 watt per gallon, when 2 WPG seems more ideal for lush/rapid growth.