I get all my info from heresay, but a VERY small contingent of top pros make 6 figures - Cedric has been noted as one of the higher paid guys, I would suppose 500 grand a year all combined at best.
Schley has supposedly been the highest paid MTB cyclist historically, the 1m could be possible combining all the sponsors and other roles. He has gotten loads of crap piled on him for it too.
The vast majority of pros - even top cats, apparently dont make great money, I heard Kyle Strait got ~50k as a salary, I couldnt attest to how much he pulls in from sponsorships and contests - didnt hear any rumors on that one.
Overall - it is not a sport you pursue for compensation; very few make a GOOD living off of it, and a great deal make enough to take care of themselves, because - as said before - they dont have to pay for bikes and travelling to spots BUT it can take alot of the love out of it when you're lugging around the world...
and then the vast majority who PAY to race ultimately. (Yes, this is MOST pros!)