there's only one flex and thats flex magazine, born april 1983.
You forgot Flex Wheeler.

At first I thought "Why would he copy someone else's nickname?" But he has definitely done the nickname justice.
As to Flex's net worth, Flex had previously considered Rich Gaspari to be a "father figure", and I didn't think he would ever leave Gaspari Nutrition. From what I understand, BSN offered him $2,000 more a month, as well as a much less intensive travel schedule. You can't really beat that. I fully understand why Flex chose to leave, and I would hope that Rich understood that too. $24,000 a year more + more time to train is extremely important for a bodybuilder.
As to what Flex Lewis is making, I can't see it being less than $160,000 USD per year, and it may be as much as a million or more, all things considered. McGregor stated that he made $40 million in 2016, and he probably made at least $140 million this year, but that gravy train won't last much longer as his brand depends on him being untouchable. Look to Rhonda Rousey to see. McGregor redeemed himself against Nate Diaz, so that made it neutral again - but with an untouchable brand, you can't lose.