A 10 gallon tank with a grow bed made from a pizza dough tray, a small hydroponic pump with timer, an air stone, rubber tubing and grommets, some pots with hydroton (small clay balls), and peet pellets for starts will get you started for about $100. If you're doing it indoors you'll need 4100k T5 lights (another $50-100). Between a hydroponic store, hardware store, and a pet store you should be able to get what you need. Be sure to get an aquarium test kit and allow for nutrient cycling before adding fish. Most folks start with goldfish. Small systems are finicky so you'll have to test PH and ammonia twice daily when you get fish. Once you get above about 200 gallons it gets much easier.
Hi Chris, you could build a 30 gallon system for "proof" fairly cheap with a 30 gallon Rubbermaid tote and a plastic concrete mixing tub can be purchased for about 6 or 7 dollars and used as the grow bed plus the cost of a pump, or you could build a bigger system with an IBC tote and use it for different stages and it could be enlarged later.
I made a small aquaponic set up to make sure that aquaponics would work for me over 3 years ago, then I made a 150 gallon and Now I have 600 + gallon system. When I made my 150 gallon system I purchased a pump that was big enough to run my 600 gallon system so I did not have to upgrade the size of my pump again. I have taken the 30 gallon system to sustainability events to show people how aquaponics works so even that was not a waste., .
It seems like I built the 30 gallon system for about $50. - 60.00 dollars, but that was 3 years ago and that did not include the API fresh water tester. I had the hydroton and shale because I had run a test system with hydroponics to see which I liked better but regular river gravel will work too. Below is a picture of my second system which was a 150 gallons
You could try something like this CHOP2 design I created: http://sketchup.google.com/3dwarehouse/details?mid=1dc612ce01c8faaf.... Just swap in your 250gal tote for the tank. It's all built from wood palettes and liner for about $750 in parts. Less since you have a tank already.