Can use the Promo sheet, but printed on 2 huge pages, which can be done at any print shop, and it costs less than $100 and is portable.

Example of Tiki poster in the wild:
http://www.flickr.com/photos/hellodarren/4060180728/
http://www.flickr.com/photos/hellodarren/4060180712/

Example of a requirement:
"will be invited to display a poster - 1x2m in size."
http://wikimania2010.wikimedia.org/wiki/Review_results

Alternative is Banner Stand

• Posters