most costly...78 USD for a hard to find color morph of a three beacon pleco
Most time consuming? the 40 dollars and 2 hours it took for my kid sister to FINALLY get the ring around around the bottle at the carnival for the prize feeder goldfish....
Most expensive so far has been $20/ea for botia kubotai a couple years ago.
I got some fry of Melanotaenia parva for about $16/ea. I thought that was a good deal for some rare rainbows.
I've lately been watching some saltwater fish I want though that are in the $100 range and have seen posts by people who have multiple fish that have cost in excess of $500/ea, so it's a matter of expectations and perspective.