I'm very interested in setting up an aquaponics system. For those of you that aren't familar, the premise is having a fish pond (in my case I want to grow tilapia for eating) and you use that nutrient-rich water to cycle through grow trays (like in a hydroponics system) and then the 'filtered' water goes back into the fish tank. I've seen the portablefarms.com website. From poking around on the internet it looks like their systems run from about $5500 and up, which doesn't include any sort of structure for it to go in.
I'm fairly certain I could set up a small tank with one growbed system, but I'm much more interested in doing something more substantial with an in-ground pond (for keeping the water from boiling) large enough to grow at least 100 lbs of fish a year.
Here is a youtube video of a beautiful setup with an computer system operating it. Definitely more computerized than I'm capable of, but shows you what can be done. I think the fish are still babies...
Here is a video of a much more elaborate system in the Phillapines, which even includes rabbits: