I'll offer a slightly different take on this: get a Launchpad & Korg Nanokontrol if you really want to DJ on a budget. It's more on the controllerism side of things, but paired with Traktor & decent midi mapping it'll give you what you need. I DJ'd with this setup a couple times when I couldn't bring my full setup.
That said, I had a couple years of DJ experience using a combination of vinyl/mixer/midi controllers, so a minimalist setup like this worked for me as I knew what I was doing.
For a quick, mid-tier price range, just get a Native Instruments S2 or S4.
And either way, get an external soundcard with the right I/O as you'll want that when you upgrade.
If you're serious about DJing longer term, invest in a nice setup. For house parties with friends and breaking into the scene, rock whatever you can use.
Honestly, you could spend $200 on a shitty mixer, soundcard, and CDJs off ebay and it'll be plenty for 6-12 months while you learn. And if you don't stick with it, well, no hassle re-selling equipment and taking a hit to the wallet. Plus, a skilled DJ can mix well on "cheap" equipment. Good gear is necessary eventually, but I don't think it's necessary for you.