Well that depends on how badly you want to be rid of them and what the market for your roosters is.
I have sold roosters for 3-5 dollars each. I have also given them free just to move them out. If i have an outstanding unique bird i will charge, if he is unruley and not good for my flock will determine if i charge and how much.
Search on craigs list now and see what others are doing.
Good luck!