On a budget check on the net for plans and read read read all the books on hydroponics you can and build your own. There are easy to build plans for aeroponic root chambers out of plastic storage boxes on line. If you are new to this start with a drain and fill system or drip system to get you started aeroponic garden systems are a lot harder to do. I have been on my quest for three years now I mite play with aeroponics this summer 2008 the drain and fill and drip systems I have built have all worked great. Most important thing buy a good PH meter and EC meter don't go cheep get the good ones.

ok. thanks for advice!

IMO it sounds like you want a series of bubble buckets. they are very cheap to build and work extremely well. as for 28 site, you can make 28 buckets or make special ones for smaller plants and group them together(like peppers).

Here is a link that might be useful: