Farrah Abraham's Gotta Pay For 'Teen Mom' Cruise

Farrah Abraham -- the most famous "Teen Mom" alum -- will have to dig deep into her pockets if she wants to board the "Teen Mom" Cruise ... which is somehow a real thing.

A spokesperson for the cruise tells us Farrah wasn't asked to be one of the main attractions for the fan event because they're aiming for a family-friendly environment. Instead they went with Maci Bookout, Amber Portwood and Kailyn Lowry.

Farrah's still welcome aboard if she has $734 for an inside stateroom or a top tier junior suite ... for $1,303.

As for the cruise ... it goes down next July on Royal Caribbean's Enchantment of the Seas, sailing out of Miami with stops in the Bahamas and Key West.