Ebay stuff is usually cheap chinese rubbish. Once you press play you will be able to see nothing of quality on the recordings.
Have you considered usuig SDI Cameras and DVR?
I often have customers who want unrealsitic things on a job. I agree sometimes you have to walk away or force the customer to understand what is actually possible and in their budget.
Also you have to be careful with wiring Batteries to Electrics from china. Usually they have no inbuilt surge...
Even wireless kits usually need cables. If you want a secure signal you really should go for a wired option, as wireless signals can be very weak when even a single brick wall comes in to effect.