Can't you simply buy a wall wart (wall transformer) to power the spy camera? Or how about a few 9v batteries connected in parallel? Those two things are alot easier than fashioning up a 8v regulated supply if you've never done it before. Do you have a solder pencil and know how to solder effectively?
Look at this set-up for a mere $60 US. It comes with everything, the
wireless color camera, receiver, power adaptors and even runs for 8hrs. on a 9v battery!
https://www.secretsecuritycamera.com/hiddensecuritycam.htm