Money in pro boxing?

Ok, I'm not talking about big televised fights with big name boxers earning millions. I'm talking about much lower down the scale; there are loads of professional boxers fighting in small events. I'm just wondering what sort of money they earn when they start out? Is it like £500 a fight? Or do they only get paid when they win?
Also how to they go about turning pro? In England pretty much all decent boxing gyms are ABA and I always thought that ABA gyms try to keep there good fighter at amature level so they can compete in the Olympics and other events. Is it a case of the not so good fighter that the ABA gyms 'let go' and turn pro?
Some sources would be got to, like websites etc.

Any help would be appreciated. Thanlks

it can be anythin from £50 to £500, in some cases a fighter will have a manager/promoter who pays the fighter a weekly wage plus his training expenses

I england you can work it out, for novice Pros, but not outstanding amatuers they get more,for 6 by 2 min rounds £ 600 as a rule of thumb