My own most exotic-looking fishes are a Farlowella and a Sturisoma. Exotic doesn't have to be rare.
A.Set up a tank with clusters of wood, twigs and fallen beech leaves. Breed Farlowella acus, not an impossible thing to do. Top-of-the-line freshwater fishkeeping.
B.Set up a tank with three completely unrelated rather large "oddball" fishes that may or may not mostly tolerate one another's company but are "rare" and expensive. Bottom-of-the-barrel fishkeeping.
You're searching for a more rewarding kind of fishkeeping. It's a good search.
You mentioned mollies. What about joining the dedicated groups that are keeping alive in aquarium populations some of the authentic Mexican Mollienisia species that are now extinct in nature, in the hope of eventually returning them to the isolated springs they once inhabited? You'd have to connect through the local university's biology department. Now that's sophisticated fishkeeping...
Any fish worth keeping is worth keeping alone, in a setup designed to put it at ease. If you can't find such a fish, maybe you should have a snake or a hedgehog...
