We hope to get a tour of the UC Berkeley Wave tank (located in Richmond) a week from Monday. We don't know how much it costs to rent. It is very unlikely that we will be doing enough wave tank modeling to justify constructing, owning and operating our own wave tank.

I dunno of anything offhand that is "completed" as such.  But you could do it yourself fairly easily for less than 150 usd + time/labor, assuming you aren't wanting a massive scale stead to work with not an 8 meter monster.  If you aren't terribly comfortable with assembly or C and lots and lots of soldering I am going to suggest you use arduino ( http://en.wikipedia.org/wiki/Arduino ) which you can get for less than 50 usd from sparkfun.  Sparkfun also sells gyros for just over 50 but I am going to recommend you forgo the gyro for a 3-axis accelerometer.  It'll make measuring a bit easier and will require you to work with less hardware in the long run.  Plus they cost less(20-35 usually).  Sparkfun(holy seven hells I seem like an advert for them, they should pay me commission everytime I mention their name) has a breakout board for the ADXL330 accelerometer for 35 dollars ( http://www.sparkfun.com/commerce/product_info.php?products_id=692 )  I am going to recommend it because it will save you a lot of fine soldering work and a fair bit of hassle.  Programming it in Arduino is fairly straightforward and interfaces with Flash if you're wanting to represent your data visually and I have even seen it interface with Second Life(which could make for some nifty seastead model interactions).

If you're interested in diy and not wanting to use Arduino for whatever reason, I have a couple of Atmega48's laying around and could be convinced to get an ADXL330 or two and prototype some boards and C code for what you're proposing.  It'd save us a bit all a bit of money and would be fairly simple to do.

Wouldn't simulation be better ?

1.  It could be cheaper. There are plenty of physics simulator that can be used. A CFD framework such as OpenFoam comes to mind in combination with a dynamics framework such as ODE . I don't know how much work would be involved in getting a general purpose simulator running. Foam is largely overkill for the kind of fluid dynamics going on at this scale... modeling physical stress would be needed as well.
2. Professional software solutions probably already exist, they may have good pricing for non-profit research.
3. Some physical phenomenom do not scale (the tensile strenght of the spar scales quadratically, the weight cubically)
4. Do they have wind in the wave chamber ?
5. Many more ideas and models can be tested
6. Shapes can be optimised, see this.
7. It can produce beautiful art.

On the drawbacks

1. It's initially more expensive as it requires a lot of qualified work, unless you're lucky enough to find a guy willing to do an applied math thesis on this.
2.  It takes more time to get going
3. It might be less accurate than direct simulation on a scaled model, but that seems unlikely. 

Holy Crap.

Better have your test protocols worked out precisely in advance at those prices, and some empirical testing in a cheaper (uncontrolled) environment (like a lake) would be a good idea too, just for simple "gotchas" even if the measurements are of only limited usefulness. This would give you a chance to practice setting up and tearing down your test model so you don't waste the time that you're paying big bucks  for.