Catching oscars from the wild (where they have established themselves in Florida due to fishkeepers releasing them) and then selling them on here hardly seems easy to me...would have to QT them, medicate to remove any parasites, then there is the trouble of shipping them, acquiring supplies, etc.
Of course, maybe you were joking
I too, live in Florida, and have tried tanks with mosquitofish...not very exciting, they are plain silvery fish, but there are some really pretty other fish. Check it out:
http://plants.ifas.ufl.edu/guide/fish.html
They will eat prepared food. Not fussy about water quality, generally. I would recommend you seek out some wild mollies - they are lovely! We have them in the Silver River here, have always wanted to make a tank for them.
One word of caution: I wouldn't assume you are doing fish a favor by taking them out of the wild. Getting eaten is part of their natural life cycle, and by keeping them in captivity you are keeping them from doing all sorts of natural things they are meant to do, such as pass along their genes. One person won't make a difference, you are only catching a handful of fish, and I believe it's important for people to learn more about their local fauna.
But taking them out of an endless body of water where competition for food is tough and then putting them in a very small (by comparison) glass box where you feed them regular meals...is not really a favor to them. Keeping native fish doesn't hurt anything, and you will probably be enriched by the experience, but don't think of it as benevolent.