i'd imagine controller you could get more bang for the buck. Two competing controller programs at the moment are traktor and serato, i'd recommend a controller from pioneer if you go the serato route. Also many use ableton to DJ, if you produce in ableton might be a good alternative to look into. I personally never have gotten the swing of it as I prefer to actually see two decks and mix between them(or 4 in some controllers). Don't know any controllers specifically in your budget.
Just know computer DJing and USB/CD/Vinyl mixers will be a whole different world of DJing, one offers a secreen and visual cueing while the other you will be strictly beatmatchning from scratch