I'm currently looking in to FPVing my Tamar.
I'm using a Mobius Actioncam, which is a 1080p HD camera. It's £40, but there are cheaper FPV dedicated cameras out there - You'll need to have a recorder though if you don't go for a camera which itself records.
Then there's a 200mw (you probably won't need more) FPV transmitter, which runs on 7-15v, which is only just inside your power setup.
The camera will usually run off of 5v, through a UBEC.
Then you have a screen at the other end attached to the reciever, which runs on 5v (yes, that way round, unfortunately!), and your screen of choice.
Transmitter and reciever cost about £50 from eBay, UBEC is less than £10 and screens start from about £70ish.