I also keep reptiles and amphibians, which can be expensive. Like fish keeping, it depends on what you have, how many you have, and how you house them.
For example, it’s quite possible to spend tens of thousands of dollars to purchase a particularly rare animal, and hundreds, maybe thousands, more on caging, if it is large. Given the expense of some herps, there is a strong motivation to breed them, in an attempt to recoup the initial outlay. Which means purchasing more of them. Then, you’re going to need a bigger house, or a dedicated building to keep them in. Most reptiles and amphibians are kept individually (unlike fish), requiring much more space and enclosures.
Then there is the cost of feeding them, which can be substantial, as the majority of herps require live prey. To cut down on this cost, hobbyists with larger collections usually culture some of their own feeders, typically insects and rodents. This requires specialized housing, space, and most importantly, time. Maintaining even a modest sized herp collection is like having a second job.
Of course, most herp hobbyists aren’t going to have a large collection of high end animals, although I think you’d be surprised by how many who do. But even a small collection isn’t cheap. As an example, let’s say you want to get a boa constrictor. Good looking and easy to handle, they are very popular in the hobby. They are available in many subspecies, localities, and morphs, but even a relatively inexpensive adult boa is going to run you $500 or so. A large PVC cage is going to run another $500 or more, plus $250 or thereabouts for a heater and thermostat. Frozen rodents to feed the snake will probably come in under $100 per year, but will your spouse appreciate your keeping them in the freezer next to the pork chops and broccoli? If not, plan on buying a small freezer.
All that, for one common, inexpensive snake. And, like fish keepers, herp keepers rarely stop at one, so multiply those numbers by however many it takes to satisfy that inner desire. For some of us, that number is dangerously high.
At the other extreme, one could pick up a used ten gallon at a garage sale, add some soil and plants, and catch a toad in their back yard for practically nothing, and still enjoy it. Like fish keeping, it’s whatever you want to make of it.