There's basically zero demand for Betamax work. (BetacamSP and Digital Betacam are a different story!)
Betamax was mostly used for two things: (1) recording TV, (2) studio releases to Beta tapes.
Many things -- maybe even most things -- have been released to VHS, DVD, Blu-ray, or even streaming media (Hulu, for example, which carries quite a few things not found on any other released physical format). The people who have content NOT available in any normal mainstream method tend to be die-hard video enthusiasts, especially given the fact that people have (in the 2000s) hung on to tapes from a "dead format" of the 1980s. They generally take care of themselves, or their own crowd takes care of them. There's a pretty big Beta hobby scene out there, though it shrinks exponentially every year, as gear disappears and people have migrated their content to other formats.
If you need a service for Betamax conversion, contact TimelessDVD.com and tell the owner that KP of digitalFAQ.com sent you. (They also do VHS work, etc -- but we'd prefer to keep that work, as those are
video services offered by digitalFAQ.com.)