How do they do it financially???

I know the big names like Mayweather make millions so they dont have to work a side job, but how do guys like Teddy Reid and lower not work on the side and make enough from boxing to support themselves financially if they fight once every couple of months?? Many fighters, even those holding belts, have full time jobs. I remember when Carlos Bojourquez stepped in for Kassim Ouma vs. Verno Phillips, they called him at the car dealership he was working to offer him the fight. Jose Antonio Rivera was livid when Ricardo Mayorga didn't make weight because he had to schedule vacation at the dentention center he works at; Jeremy Bates had his insurance card up on FSN when he fought Holyfield, the list goes on and on and on

Split costs, investors, loans, work, ect.

Glen Johnson worked on a construction site, that much I know. Then he started making five figures for a fight.