You r in z best position 2 get high contract salary

Since you passed interview, and you are sure the client company is willing to hire you, so you are in a good position.
Try to ask the Agent a hourly rate which you feel happy with.
The Agent will make you happy if they can.
Otherwise, they will lose the business, and they have no reasonable explanation to the client company.
Usually the Agent get 30% as their commission.
Thanks!