TTC DVD set is regularly $99. As a Pelican, it's $89. Their website has a page that lists all the perks of membership. Discounts, office hours where you log on and listen in on a discussion about various topics, radio read along audio books, teacher guides, discounts to their online academy classes, discounts on classes for parents, etc.....
I've been a member for a few years and it's been worth it - particularly if you have kiddos that might take a class. If you just want to buy TTC, perhaps not.
I'm sorry - I'm not sure what the discount is at the convention, but I'm sure if you emailed them, they'd be happy to let you know.