How do i recruit prisonners? When i tried to recruit they said that i have to pay them a price but did not say what they want. I remember that they wanted stuff like 2k coins for recruiting but now its different.

the easiest way is just get them to "worships you" affection.

you can do this by talking to them, giving them the gift they prefer, and over time from your keeper/ warden.

once they're at "worships you," when you ask them to serve you, they'll join for free.

Or the simple way to get them to the Worship status is to simply screw them until they get to that point, prisoners can't resist (servants can & typically won't agree to it before at least being at the Love level unless they have the Perverted trait).  This does take a while to do from lower relationship levels however, so you could always find something else to do while the game does it's thing & eventually maxes out the relationship level.

EDIT:  Alternatively, you could just wait if you aren't hurting for more servants or running out of prison space, their level will increase over time just by staying in prison waiting to be released (normally I'll strip them of all their equipment while imprisoned, not sure if that has any affect or not however).