Does a S3D production cost twice as much as a standard 2D video?

No!

Naturally, costs vary with each project, however, the cost difference is rarely more than 20% below-the-line. The added cost is for some specialized equipment and personnel. Also, 3D takes a little more time to produce because there is an additional optical axis to consider.

"X" represents horizontal, "Y" represents vertical and the "Z" axis represents the depth. It's the "Z" axis that produces the dramatic off-screen effects.