adwords ppc

Hey, what is the lowest you paid for a conversion? I mean how much you paid to make a certain amount? People keep saying average profit margin for ppc is around 35-40% of the total ad spend? Can you give some tips who are doing high in even numbers?

I am doing adowrds PPC by buing CC nowtimes it's so tough for suspended ratio. Is facebook have any method like adwords? I mean if i will buy cc and add on facebook then can i get any threshold like adwords? Is it possible or do you have any method like this. Please share it will helps me a lot...