In the States, extra payment for work outside your regular workplace is usually called
per diem.
per di•em
(pər ˈdi əm, ˈdaɪ əm)
n.
2. a daily allowance, usu. for living expenses, as while traveling in connection with one's job.
Perhaps the exquisite and rare adjective "quomodocunquizing" will suit your need. And, it does not have negative overtone, it is very much neutral. You can use it in all possible registers: greedy politicians, greedy businessmen, greedy youngster, greedy person, or greedy society etc. You can also use it in your essay title. It is an adjective defined as,
that makes money in any possible way
Merriam Webster referes it as an archaic (and not obsolete) word. Check side note: https://www.merriam-webster.com/words-at-play/patriotism-vs-nationalism
So, if you are driven by the desire to accumulate wealth by hook or by crook you are an "quomodocunquizing person". You don't have to be a criminal or mafia to do so, you can be quomodocunquizing businessman.
Also, if you prefer, then you can use materialistic. It is an adjective and has a somewhat negative connotation.It is a synonym of "money-oriented". Being a materialistic or money-oriented isn't an acute negative thing in the contemporary world, isn't it?
Merriam Webster: https://www.merriam-webster.com/dictionary/materialistic
excessively concerned with material possessions; money-oriented.
"we're living in a highly materialistic society"
Reference link for the word: quomodocunquizing
citation 1: Official twitter of Oxford English Dictionary
citation 2: New York Times - Daily Lexeme
citation 3: Book- There's a Word for It (Revised Edition): A Grandiloquent Guide to Life
citation 4: Book- The Horologicon By Mark Forsyth
Best Answer
It is often called: dirty money:
(AHD)