They can be incredibly high. I've found our local barcamps to have been a mixed bag, and it really depended on the quality of the people who showed up that day. They used to run it where everyone pitched during the morning, then self organized around the pitched sessions. That made the sessions totally up in the air - you had no idea when you woke up if it was even worth showing up. Later ones set up early pitching/voting on the web, which seemed to help some, but because there was no ticket cost, the organizers were still on the hook trying to determine food cost and such in advance, when just a little bad weather might keep away loads of people.

The area ncdevcon.com (next week in Raleigh) started charging for tickets this year - a nominal $60 for 2 days - precisely because when it was free, people wouldn't show up on the day because they had no real investment.

For indieconf.com, we've charged - both for last year's even and this year's event - and are posting speakers/sessions well in advance so people know what they're getting.

There's room for all styles of events, certainly, and perhaps I have bit more invested emotionally than others, being an organizer myself, but the barcamp self-organizing doesn't always produce great results. This may also have something to do with geography as well, but I don't think anyone's done an actual study of barcamp attendee satisfaction around the globe. Maybe that's something you could add to lanyrd :)