Ok,
SUBSTRATE: you can change all your substrate in one go, you don't need to worry about your bacteria growth as the majority of this is in your filter. remove your fish and water, i put them in a large plastic rubbish bin (new and cleaned of course), with a heater and filter as the job can take a couple of hours. EcoComplete will cloud up your tank big time so replace the water very gently, use half your old water and half new, i put a large bowl on top of the substrate and pour the water onto that which drastically reduces the cloudiness, another little tip is to slope your substrate towards the back, this gives a deeper appearance to your set up.
LIGHTING: Aim for around 2.5WPG (watts per gallon), T5 is great but slightly more expensive but assures that light will penetrate the very deepest parts of your tank, a very good and affordable light is the Hagen GLO T5HO.
FERTS: Well your options are endless here, but most people including world class aquascapers use Tropica Plant Nutrition +, this supplies N, P and K and is widely used as a sole nutrient supplier. Note that Nitrogen and Phosphorus should only be used when plants are thriving so when your setup is new you should stick to standard TPN, not TPN+, then introduce the TPN+ slowly. Don't follow the instructions on the box, if you have a heavily planted tank (70-100% planted) then use anywhere between 2ml to 5ml per day, dose daily and at around the same time as plants appreciate a constant routine, you can mix TPN and TPN+ if you like. You can also use Tropica Plant Nutrition+ capsules for direct root feeding - these last for up to a year so are relatively inexpensive and are great for particularly hungry root feeders.
CO2: $500 is a lot, you can pick up a great Dennerle 300l system complete with everything except a solenoid, drop checker + 4dKH solution and diffuser (well it does supply a flipper diffuser which is a ladder style and its absolutely hideous!!!) for £140 which is just over £200 US, with the things not included you'l be looking to pay around $250 US. If this is out of the question then you will still need some form of CO2, you can do this DIY, here are some links:
<a href="http
/www.fishforums.net/index.php?showtopic=212550" target="_blank">http/www.fishforums.net/index.php?showtopic=212550</a>
<a href="http/www.fishforever.co.uk/carbondioxide.html" target="_blank">http/www.fishforever.co.uk/carbondioxide.html</a>
or you could down the nutrafin route which is very cheap (obviously no where near as effective as a pressurized system), you would need 2 or 3 of these for a heavily planted 55G:
<a href="http/www.fishforums.net/index.php?showtopic=164548" target="_blank">http/www.fishforums.net/index.php?showtopic=164548</a>
If none of these suit then you could go for liquid form with Easylife EasyCarbo or Flourish Excel.
Hope this helps, good luck.
