Then we talk about budget. I believe you should think of entertainment in much the same way as you think about the food -- on a per-person basis. Is it worth $3.00 per person? $10.00 per person? Like everything else in life, there's a "get what you pay for" principle at work in the pricing of performers. Most good professional musicians get $200.00 and up, which makes a 6-piece band well over a grand -- often much more on prime dates. I often advise those who can't spend more than $500.00 or so to get a good DJ; what they might lack in live energy they make up for in sound quality and variety of music.
An experienced planner once explained to me that she always budgets entertainment ahead of other things, and if you think back to the last several weddings you attended, you'll probably agree that the entertainment (good or bad) stays clearly in your mind.