The difference in pricing between your local friendly expo and Nine Worlds is because of a major difference in content and business model. MCM and similar expo-style events focus primarily on vendors and paid autographs. While there may be some workshops and guests, they're a small fraction of what you'd find at a residential convention such as Nine Worlds.
We've got a large number of simultaneous content tracks with their own curators, each putting together a set of panels, workshops and activities that reflect their fandom or area of interest. Additionally, guests at residential conventions are expected to take a fuller part in the programme, and ideally to be a *part* of the convention rather than being whisked on-stage and then off again after their panel. We've got a film festival, gaming tables, social gaming with nerf guns, and a full evening entertainment programme with music, parties, and more gaming and discussions.
This focus puts us more in line with residential conventions such as Eastercon, Worldcon, Redemption, Starfury and Massive Events, all of which cost a similar amount.
TL;DR Geek festival, not geek market.