What research has examined the cost in time and money of conference attendance? I am looking for surveys/studies that quantify the time and money academics spent on conferences/symposia/workshops/etc by both organizers and attendees. Specifically, I'm interested in both academic and institutional costs related to conference, travelling, and administrative tasks related to travel. (In my experience the overwhelming majority of expenses are covered by employer/grant/etc anyways.)

I am most interested in the field of computer science, and academics affiliated to US institutions.
I published a paper:
 Anderson, L., &amp; Anderson, T. (2009). Online professional development conferences: An effective, economical and eco-friendly option  Canadian Journal of Learning  Technology, 35(2). 

in which we calculated the costs (transportation, hotels, meals etc.) in dollars and in Carbon costs using a medium sized conference in the UK.
We were interested in showing the HUGE cost and carbon savings if the conference was held online and used this data in our book on Virtual Conferences.