That sounds pretty steep! Sure, the mother plant will give you a harvest of Anubias under ideal conditions that you could sell to recover the cost, but $50?!! wow!
I bought an Anubias Cofeefolia from www.aquaticplantdepot.com
for $6 and it has grown into a huge "mother" plant. It has produced five new rhyzomes in one year, each with almost a dozen leaves. They have "show" Anubias at that site as well, that are most likely just as good, or at least close, to the mother plants you found. And they're only $15.