why not try this.... a 10g native tank. i found all these animals 20 mins from my house. just bought a few pieces of live rock from the lfs and was done. i think all in it cost me £45, including all the equiptment and tank.
you could do something similar, go to the beach and catch your own fish.
i just have a few gobies and 3 beadlet anemone's (called red anemone's on ebay and apparently from tropical waters), with prawns and snails as a clean up crew.
go easy on me though. its my first SW tank... but what a tank eh? especially for £45