Had a bit of a look at one of the cheapies, the main problem is lighting at that depth. If you can get one that has a quality light system and high quality camera, no worries. You may be disapointed at the quality of the picture otherwise.
Bloody good idea though!!
Some of them have a keel on them so you can troll them behind the boat as well. Would be awsome to watch tuna, macks etc taking the lures and baits
The better ones cost a fair bit though
Regards, Tony