Because different areas have different price ranges, and different couples have different needs and budgets, it isn't possible for me to give you a definitive amount.
The best guidance I can offer is directly related to the following factors:
Do you want your guests to be able to hear the ceremony and vows by using an additional sound system not provided by your venue?
How important is the success of your reception to you and your fiance? Do you want classy intros, someone who entertains (as opposed to interrupts) your guests, unobtrusive sound systems that won't look tacky in photos and great music & dancing for your reception? How things sound and how successful the dancing goes is especially important if you've hired a wedding DJ.
If you haven't hired a professional wedding coordinator, do you need the DJ to help you create and execute your wedding day timeline to make sure all of the introductions and announcements are made at the appropriate times? Are you going to count on them to ensure that the photographer and videographer are in place for elements like the toasts, cake cutting and first dance?
Do you want a DJ you can trust? That knowing they are there will give you peace of mind that everything is going to go smoothly and that their presence will positively impact the success of your wedding and reception?
Have you ever hired the wrong person to do an important job? You didn't realize until things went wrong how important it was to you. Or maybe you were just too busy to be overly concerned and thought you could get by. Whatever the reason, regret basically sucks when you know you could have had a better outcome if you had done things differently.
If the answer to any or all of these questions is yes, you will want to hire the best, most Professional DJ you can afford. What do good DJ's charge? I will say while there is always the possibility you can find a better than average DJ at any price point, if you want a really good or great one they will probably charge at least twice as much as the average estimates you'll receive.
I hope this post has explained why and that I've made the process of locating, recognizing and qualifying a good DJ easier for you.