Awesome, awesome thread with tons of great advice! We have a local con coming up this weekend and my son wanted a Sam Flynn costume, so I dug through the posts and got a game plan and whipped this up last night. It's a slightly oversized turtleneck ($6), some ladies black leggings which I sewed to fit him better ($6), 5 sheets of black craft foam (99¢ each) and 10 feet of reflective tape ($13) ... oh, and he got an identity disc while down in New York with my wife visiting friends.
Low tech but really cheap and comfy and he's psyched!
When he was standing in front of the Tron mural I painted him, he said "It's like I'm looking into Kevin Flynn's past!" Weird kid ... but of course, what hope did he have with a freak dad like me.
Thanks for all the awesome research people!