Last year I attended my first comic book convention. Paying for the badge was $30 (single day) and bought a couple of Marvel Red Hulk Action figures for $40. Lunch was $8 and bus ticket fare was only $3.50 (got a ride back from a friend) So I would say $81.50.
...I think we've managed to get into a few of them for either discounted prices or for completely free. Usually my dad is part of a table, so either we pays a portion or he gets covered. Shoot, I know at the last one we went to my dad ended up getting really cool with the guy who runs tables or whatever, so now he can get in whenever he's got something to show off.