true, I am currently running to tanks, on a 21L NZ mudflat marine, the other a Leopard fish breeding tank approx 50L (with more on the way) my total outlay so far has been $15 for the marine tank, $5 for the Leopard fish, $3 for the light tube, $5 for a hacksaw to remake the light fitting, total $28, and a heap of fun!!!!ok they not the prettiest tanks, but they are interesting, fun and I've fallen in love with my sand goby.
last time I think it cost me around $250 to set up 8-10 breeding tanks, with fish included
so budget is all in your own head. get creative, its the kiwi way
p.s. just noticed the Crayfish tank in Sanfords is running an under-gravel filter connected to its sump, the under-gravel filter is made out of some shade cloth held down with 5 big stones