man i cant believe that my little ass truck failed smog.. i need a cat and maybe even an oxygen senser. so no since ill have to replace the cat i started thinkin well lets just do a full cat back system. so first off im a cheap ass haha soooo whats the cheapist cat back system i can get orrrrrrr who knows where i can get a cat for under 100 bucks

Low Range Off Road had cats for $99 plus shipping. I got my high flow cat from a local muffler shop for $60 but he also did the exhaust for me so he may have gave me a break on the price . He went from the exhaust maifold back, new O2 sensor, high flow cat, and a cheapy (sounds good) turbo muffler for $250. Now the exhaust manifold has a crack in it,....time for a header!

are those cats legal for california?? im hoping that its just an o2 sensor but if it isnt then thats what ill be doing if i cant get a cat back system for cheap...

If you want the cheapest cat back system possible, your going to have to build it yourself.  The labor is the killer when it comes to getting kits like that.

I would check with your local exhaust shop and look at using a high flow cat and basically the same setup sklope mentioned with 2" and expect to pay similar.  If you need to replace your cat, you might as well replace the tubing from your header back at the same time.

Is this for a Tracker or a Samurai?

If you are in California then try submitting an App to C.A.P.   They will give you up to $500 to repair the smog issue.  Here is the link

http://www.bar.ca.gov/80_BARResources/01_CAP&GoldShield/Factsheets/Consumer_Assist_FAQs.html

What part of the test did you fail?