WordNet records no synonym and no antonym for finder's fee. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a fee that is paid to someone who finds a source of financial backing or to someone who brings people together for business purposes
“the agency got a finder's fee when their candidate was hired as the new CEO”
Synonyms, antonyms and the broader and narrower relations for finder's fee come from Princeton University’s WordNet. Full sources and licences.