how much money do FBI agents make a month/year?

Not much, it's enough to live but you won't get rich, but they get hella lot of benefits

American government employees don't make much unless your a politician and even then unless you get into the higher areas of it anyway if you want to make good money work in the oil industry on drilling rigs as a derrick hand or driller they make upwards of 120 000 a year if you were Canadian you would make more money doing that I myself am lead field technician for an oil and gas well service company and i make between 100 000 to 140 000 a year depending on how busy we are

Maybe the answer is here.

http://www.fbi.gov/