Not in money, sure, but there's a non-monetary cost to sitting alone with a sign for a few hours.
Edit: Before anyone says it, YES, I'm still planning to do this, and how I'm going to do this -- I'm not indefinitely digging up excuses for not doing it. I'm just listing a concern. I've far too often heard diagnoses that would interpret my remark otherwise.
Sit there with a sign saying "LW" and a big picture of an Art Lebedev paperclip. If strangers ask you what you're there for, say "I'm meeting friends. Have one of these." and hand them the tract version of The Twelve Virtues Of Rationality. At worst they don't bug you, at good they read it, at best they stay to argue!
Heh, I've just edited in (and then out of) the grandparent comment, "even though I disagree with the judgment", then thought it's more likely specific to me and for a random person it would be correct that it won't cost them much, then that I voiced that incorrectly (I won't mind waiting, I'll always have something to think about or something to read, but I'll probably not like a meetup), so technically speaking it won't cost me much either in that sense, but I probably won't do it.
Pick a time, pick a place, declare you'll be there with a sign reading "LW", and I'll promote it to the front page. Either someone else will show or they won't.
Even for Waco? Waco???