I'll give you the sage advice that has been given to this question for years, then I will give you my experience.
Heres the main advice you'll get from current and past DJs:
Save up and buy quality decks.
If they still made Technics I would advise you to pick a pair of them up. Check craigslist and stores to see if they have a good set available. If you go with a set of new decks, check them out in the store. Aim for a direct drive system, not a belt drive (do they make those anymore?) Start and stop the deck a few times, how fast does it get up to speed. How heavy is the platter? Does it move around (up and down) when you touch it (imagine back queuing the record, can you imagine the platter bouncing and knocking the needle out of the groove? Do you have anti skate and height adjustments on the tonearm? (all decks should have this, if they dont ... )How stable is the deck, is it heavy or plastic? Basically you are looking for quality here. Any current DJs out there can suggest some specific decks for you, currently I have a set of MK2s and some TT-1s. Nice heavy units, stable, no platter movement, good recovery from scratch/back queue, start/stop etc.
Do most artists use MP3 decks?
In addition to my decks, I also have a Bheringer BCD3000 that I have used with Traktor. I can honestly tell you man, it works, but it is NOT the same feel as playing with vinyl. I think any vinyl DJ would probably say the same thing. For me it is just not the same feel, and it is not as fun. That being said, it is definitely an option, and it works really well. A lot of folks use mp3 devices ... including me ... but given a preference, Id rather throw on some actual records.
You also have the option of using timecoded vinyl. Check out the Native Instruments Traktor Scratch set and Serato scratch live options. With these basically you have a set of vinyl that can be used with an audio interface to control the Traktor software. Sort of a blend between MP3 and vinyl.
Now heres a super quick bit about my experience:
On a whim (after hearing Metalheadz Platinum Breaks v2) I went out and purchased a DJ in a box set. I think it was a stanton straight-8 belt drive set. Probably cost me about 250$ or so. They were awesome. I could totally stop the platter by pressing on the spindle (this is a bad thing), and platter drags and back queuing could totally start reversing the platter ... especially with a couple of beers in you. Despite these pitfalls, I really really had a lot of fun on these decks, and I got quite good on them after some practice. this was great until I started to get booked to play parties. The standard at a party (at that time) was Tec 12s ... lightyears away from my 250$ decks. It was a huge learning curve and I really wrecked the first couple of gigs that I was at. Quality decks are so much better than the cheap ones. For example, try to stop the platter on some tecs by grabbing the spindle. Without some vice grips you wont be able to do it. So this was a bit of an eye opener, and I eventually started practicing on my pals tecs instead of playing at home so I could get used to how things worked with quality gear. Essentially I had to relearn how to beatmatch .. and then repair my Dj name after stinking up the dancefloor.
In short: buy quality - you will have a lot more fun and you will not have to relearn any bad habits that you learned on low quality gear. Take the time to read reviews (with a grain of salt). Take the time to spend some hands on time with your purchase before you buy it - you are going to spend between 300 (low quality) and 1200 (high quality). make sure you are getting exactly what you want!
In any case, best of luck. My time spent DJing was probably some of the most fun years in my life. Also, get yourself sorted and comfortable, but dont let drugs and the opposite(or same if thats your thing) sex drag you down. Seen a lot of good friends go down that road and never come back.
