Communications infrastructure is the latest backbone for commerce and recreation. Both large parts of conventions. I am sure that everyone would really Like the ability to check their email, tie in to distributed communications and notification services, and battle in area/internet DS games. Dealers may want to tie in to their remote servers to report inventory, schedule resupply of hot items, or even use encrypted online processing systems instead of hardlined phone connections for credit card/debit transactions.
I estimate that if each convention goer needs an Average of dialup speed (2-3kbps), and there are 2000 or so convention goers daily, then even without a transparent proxy server, a business class connection (4000-6000kbps down and up) should suffice. A proxy server, unfortunately, would not make any impact on the requirements for interactive communication, but would lessen download bandwidth slightly for more static (Automatically determinable) items.
As far as it being a third party, it may still be possible for us to reach an agreement where whatever profit the hotel expects to see, and whatever operating costs exist, plus typical profit if the convention decides to boycot all but 'try me for free' internet, over the pro-rated period that we have booked the hotel. I think that number MAY be less costly, and will almost definitely be less of a pain logistically, then anything but a business class DSL/Cable connection (if we would even be able to negotiate setting one up.).
