After reading loads of posts and watching hours of Google hangout video talking about tethers, a whole range of use cases keep coming back to me with one thing in common: autonomous operation. The absence of a tether necessarily limits the ROVs time on station UNLESS it has a way to recharge.
A quick Google of "floating power station for ocean vehicle" came up with a neighbor of yours, the Monterey Bay Aquarium Institute (MBARI). They have just such a power-generating buoy put into use in 2012. From the project's website, "The dream: an underwater charging station" is identified as an explicit objective.
On the rash assumption that your two efforts may have some common goals and may not have communicated recently, let me gently nudge you in that direction. There's a good chance MBARI would welcome an ROV that's inexpensive enough to allow for an eventual swarm of them to conduct more research than MBARI could dream of doing without such a platform.
But dont stop there: think how much fun it would be to program higher order "autonomous mission profiles" (e.g. "find and track large mammals") and how much fun it would be to develop instrumentation packages (sonor?) that would allow for these sorts of missions.
If you guys have already explored this with MBARI, I'm sure everyone would love to hear about it.