2 cameras, two sets of identical lenses, grip that can carry two cameras (usually a 3d rig), and the most expensive part - people that know how to work with 3d.

2 cameras, two sets of identical lenses, grip that can carry two cameras (usually a 3d rig), and the most expensive part - people that know how to work with 3d. That usually means a stereographer on set, more storage, dedicated 3d dailies preview (special equipment, monitors), DoP that knows what he's up to (3d requires slightly different lighting setup). All combined isn't THAT more expensive on A budgets, but usually they shoot with parallel setups of two or more cameras (double for 3d). With special monitoring, extra step (stereographer) and slightly different lighting techniques you're looking at more time needed for each setup - which then halts everything and costs even more money. And that's only for production. Postproduction has to work on everything twice, including rendering... so it adds up.