i spent $40 on a Chinese Hi Fin Banded Shark for my indoor pond. but I also spent $80 on a proven pair of mating africna knifefish, haven't got them to mate yet but im hoping that they will.
the most i spent was £350 or around $680 usd for my RTG asian arowana.
i have spent as much as that again on tigrinus as i have a knack for killing them.
i feel i got a very good deal on my arowana only a few months before they were selling for around £600 - £900.
Most exp. fish I have seen in person was a 3 ft ghost knife $150
Most expensive fish I have actually been tempted to buy was a full grown mbuna puffer for $75.....It is a cool active fish, but I bare have an aquarium it could fit in much less live.