Thats a great question! Pricing on DJs varies greatly. DJs range in pricing from $350 to $2500 (or more) for a typical 6 hour wedding. All DJs are not the same. While your cousin may have had good luck with DJ So and So for $350, you may not. Like many things, typically, you get what you pay for. If you want a PROFESSIONAL with professional equipment (and backups), legal music, insurance (most venues require this), and experience you're not going to find that in the lower budget ranges. You should plan on spending about 10-15% of your total budget on entertainment.
While you may think you're only paying for a "6 hour package", in reality, most DJs will spend about 30 hours on each wedding. From consultations, music preparations, rehearsals, to the day of. Your DJ will probably have at least a 12 hour day for a 6 hour wedding. Packing the truck/trailer/van, driving to the venue, unloading the gear, setting up the gear, performing the ceremony/cocktail hour/reception, breaking down, loading gear, driving back home and unloading the vehicle. Its a long day, all of which he/she is paid for. For most weddings, we'll get there about 4 hours from start time. That allows us enough time to set up the ceremony sound system, reception sound system, lighting, and wireless uplighting. We are able to break it down in about half that time luckily.