I am just starting. What exactly are the costs for me to use ad hoc?

The £2.31 a week maintenance fee is paid by all members wanting ad hoc rooms. Contract-only rooms do not pay this fee.

Are the rooms the same price?

Yes

I want the security to have the same room same day every week, is that possible?

Sure, you can book the rooms out for a whole day, half day or week and if for example you have a change of plan and don’t need the room you could put your available hours on the booking system and get the money refunded.