Wherever you get them and however much you pay, just be sure of one thing. You give yourself plenty of time to get everything setup correctly. I built a bar for my wedding and did not have my lines hooked up until about 3 hours before the ceremony. I was scrambling to fix leaks and the like. It was stressful. And I did not have time to troubleshoot any foam issues and the such so a friend of mine kept messing with pressure, over pressurizing and purging. And then set the pressure too low. So by the end of the night I had a keg labelled empty but wasn't and I ended with a fresh 5lb nearly empty.
Also, just for reference, I had three 5 gallons, a 15 gallon and about 200 bottles for about 150 people, plus bottles of wine. It worked out to be enough, but likely because we also said some beer and wine will be supplied but also BYOB for when we run out. If it was not for the pressure mistake my friend made, all but a few bottles would have been gone.