I've heard many stories of horrible DJs who have played the same song twice, played the unedited version of a vulgar song when all the music is supposed to be clean, played the wrong song for a father/daughter dance, or had their laptop crash with no other way to finish the wedding. These types of mistakes are inexcusable and should be considered when choosing a DJ to perform your wedding.
Here's just one example of why you get what you pay for:
So, please consider hiring a DJ with a proven track record, that is professional and don't sell yourself short by going the cheap route.