First thing:
How large is your street kart?
Is full suspension out of the question completely or is it a possibility?
Harbor Freight Vulcan wire feed welders are cheap and easy to use. Recommend getting one that accepts shielding gas, in the event you want to use solid wire instead of shielded flux cored wire, as solid wire is cheaper than flux cored.
Pipe isn't the best material for frames. Its heavier than what is used. What you want is tubing. Most use square tubing for a go kart and mini buggy. It's easier to work with than round tubing. 1" outside diameter tubing is the starting point at 11ga thickness (about .125") and smaller like 14ga. I'd go with 1"x1"x11ga square tubing.
Pipe is measured by its inside diameter, where as tubing is done outside.
You're going also want a saw that can cut steel easily and straight...so either a chop saw, bandsaw, or even a sawzall with a straight edge guide to help it cut straight.
You have several metal Supply shops in the El Paso area. These will be the best places for metal because they sell it usually by the foot or pound at a much cheaper price than say Home Depot, Menards, Lowe's, etc.
El Paso Metals & Supply
Aarmor Metals & Supply Inc
Chaparral Steel Supply
These are the places I'd call up first thing Monday when you get a chance to.
