Another great way is to breed a bunch of speckled leaffish. There are 8 different combinations that can get it using only common fish:

Twinfin Spotanus x orange fruitfish
Twinfin Fruitfish x orange spotanus
Twinfin Beta x orange stickfish
Twinfin stickfish x orange beta
Greenfin beta x spined stickfish
Greenfin stickfish x spined beta
Greenfin fruitfish x spined spotanus
Greenfin spotanus x spined fruitfish

Speckled leaffish will last between 110 - 130 or so years in a tank with no environment research and no seahorse. that's long enough for lots of breeding. And if you sell off the older ones first and keep the younger ones you'll have no problem. I can get over $100 per speckled leaffish.