Depending on what kind of Africans the "4" were and the overall condition of the fish...
When I had my store in Virginia I would have given you $35 store credit or cash max unless you were a "known" good customer. That price is based on the "market" in Virginia at the time.
Oscars...$5 credit each.
Cons...$1 each (unless they were massive)
4 "common" Africans $2 each (again, unless they were huge or uncommon)
$1 each for the Zebra fry.
Back then you could barely give an Oscar over 5" away and Cons (even good sized ones) were only $2.49.
So all in all I would agree that you got rooked but not horrendously.