I bought, pro pecunia comparavi, mercatus sum (3)
I believe the answer is:
emi
'bought pro pecunia comparavi mercatus sum' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'i' is the wordplay.
I cannot quite see how this works, but
'i' is within the answer.
The remaining letters 'em' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for emi that I've seen is " Record company".)