I have 0.0.1 ball python, and that's it! Because I'm a college student, my income is irregular and mostly depends upon when I can get an appointment for a medical experiment, so one snake will be more than enough until I have the time to get a steady job. With one bp, the initial costs were over $200, and I estimate an average of 2-4 dollars a week on food for it's first year. Vet visits are $44 for healthy visits, and $16 for a fecal, so at least that's not over-the-top.
The bottom line, really is just to be realistic about the amount of herps you can afford. A lot of people *can* afford 18 herps, but for those of us that aren't at that stage in our life yet, the hardest thing is to restrain ourselves from getting that cute little leo that is on sale for "only" $19.