Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Read Diana Walstad's Ecology of the Planted Aquarium.
That book will help you figure out where you can economize and where it is better to spend a little more up front and save over the life of the tank.
Cheap substrate with no cationic exchange capacity (ie sand, gravel) is very cheap to set up, but it does not hold fertilizers so conditions in the tank can be inconsistent for the plants, possibly leading to algae, or constantly having to add fertilizer.
Better substrate (still cheap) with high cationic exchange capacity is just as easy to set up, but moderates the fertilizer availability for a more even amount of fertilizer to the plants.
Mineralized Soil (not covered in Diana Walstad's book- look for it here in the substrate forum) means adding just a few additives in the set up for a long term healthy tank.
I would like to suggest that you get a different shaped tank than the standard 55. The standard 55 is very narrow front to back, and very tall. This sort of shape is very difficult to light and to 'scape.
Look for a tank that is not quite so tall, but is pretty much as deep front to back as it is tall. The 'breeder' style is like this. For example, a 40 gallon breeder is 3' long x 16" deep x 16" tall. This makes the tank a lot easier to get a 3 dimensional effect from rocks, driftwood and plants. More room to arrange the things in front of and behind each other in layers.