How much are they PAYING the plants?

I am just wondering how much they are paying these people to go into these jails? It can't be for free or none of them would go for that long. A week or 2 maybe but not 2 months. Plus you also run the risk of having another inmate rig you up or plant something on you, on your bed, start a fight with you, and then you would be looking at REAL jail time. Why is it worth it?
I wouldn't do it for a million dollars, well maybe a million but not anything much less.