I thought this would be an interesting thread to start, and would also be useful for folks considering adding new pets to their household. Those who keep good economic records, or know reliable sources, can add species to the list. Folks will have a rough idea of how much of an economic investment a pet represents.
I'll start off with one I found recently, complied by a boa constrictor breeder:
The cost to keep a boa constrictor, which takes into consideration the cost of the animal itself, caging and environmental controls, bedding and food, is as follows:
$2400 roughly (or $4950) over 20 years or an average of $120/year or $10/month (or $248/year or $21/month).
Variables include possible vet costs, various other husbandry supplies, shipping for rodents, etc.
This figure would also be pretty accurate for other similar-sized constrictor snakes, such as rainbow boas, larger carpet pythons, etc.
So, before you consider bringing home a new pet boa, consider whether your budget has room for another ten to twenty dollars per month. (Obviously, a big chunk of that expense will be up front, in the form of the cage and equipment, and the animal itself, but monthly expenses begin immediately).
Another thing that you can do with figures like this, is save up the full amount in advance, and put it into savings. You can then draw on it over the years, and have some confidence that you'll never be left without a means to care for your animal if times get rough.