Hi all,

I need a low cost usb audio interface that will meet

My Needs:
1) Price - Low as possible
2) For Working with Native Instruments Traktor Pro and Kontakt/Massive at the same time
3) That could handle live DJ Sets(no latency etc.)
4) That has an instrument input for a guitar/mic - although maybe I can live without this feature if it will make the price much higher.

My System
Lenovo G570 4334
Edirol PCR-300 Midi Controller

Options
I found this Numark product: DJ|iO USB DJ Audio Interface | Numark - Cutting-edge professional DJ equipment
I think I can get it for 50-70$ on ebay. that's the product that fits my needs best from what I've found so far but maybe you guys have a better option to suggest :)

Although I don't do any DJ'ing, I just got this Focusrite Scarlett 2i4 which they advertise as DJ-Ready Outputs (4 RCA outputs) and is a really good audio interface. You can check with Audiodeluxe to see if they will give you a better price than waht's on the internet (new item price)......they did for me.
 
http://us.focusrite.com/usb-audio-interfaces/scarlett-2i4
 
Best of luck!!

Lowest price I found is 143$.
I was really hoping for smthng between 50-100 $ but thanks for the tip anyways :)

$50- $100 will get you a good sounding interface with bad audio drivers. $150 will by you something you can depend not to crash your show. 

What would you recommend for $150 cactus?

I can't "recommend" anything I've never used. But the unit mentioned above does seem very popular these days. That's a good sign. The connectivity would be important for me. And that the drivers are well documented as excellent. Some cheaper interfaces don't even have proper drivers, that's what I was getting at above. Drivers are way important.