That's quite a difference, and it would be very tempting to choose the cheapest alternative. If that's all you can afford, than you have no choice. But, consider the law of supply and demand. There is a reason some DJs can charge more money than others. They are usually worth it.
More expensive DJs tend to be the more experienced DJs.
They can charge more because they are in demand and they have a good reputation. Generally, the DJs on the low end of the price scale are new to the business, and trying to get established. They could do a great job, and might be worth a shot if your party is on the informal side. But there is definitely more risk with a less experienced person. When it comes to a special event like a wedding, or other types of parties, you want a professional entertainer, not crossed fingers.