You know, if you invested $50.00 a month every month in a mutual fund or other vehicle, you will have in 20 years far and away more money than you would get by breeding the snakes you mentioned every year for 20 years.
Please don't enter this hobby for money, because you will be disappointed. If you want to breed snakes, pick those types you are interested in, and do your best to produce the healthiest babies possible.
This advice comes from a guy (yours truly) who spends far more on cages, food and other snakes than has ever made selling snakes, so keep that in mind too.
But, if you are bent on having an investment snake, get into something that everyone doesn't have everyday access to yet. Hypo Pueblans or albino Hondurans come to mind. In this case, you will need to lay out $1000 or more, but at least when you do produce babies there might be some interest. Remember, it wasn't that long ago that albino nelsoni were $1000 a pop. Now, people offer them for $150.00 and the snakes still don't sell as quickly as they did when they were more expensive. I wish I would take my own advice on the hypo Pueblans, but I'm too stuck on locality rosy boas and odd stuff like rubber boas that aren't worth money but interest me to no end.
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Mark 