SMS pva provider question!!

Hi guys,

I have seen numbers of guys here looking for mobile phone sms verification its always looks hard or expensive, real SIMS numbers to verify accounts , whats the price range to provide that and how i can start it up? whats the dynamic between provider and buyer? its like msg me online requesting and i provide the verification code ?! i have authority to have real numbers/SIMS.
any clue/advice, links to other posts will be appreciated.