I worked in the music world for about seven years, and during that time I learned that booking your favorite band is not a cheap thing to do. The good folks at Pricenomics received a list of estimated prices (asking prices from a third-party booking agency) for what it would cost to have a band play at your event. As you can see, the prices are not cheap but based off of experience it isn’t easy to grab someone like Kanye for half a million. Still, this gives you a good benchmark.
