Pilot00 makes an interesting point using the canaries.
I had cats for years. They didn't cost so much. But then I moved to a city, later lost my job, and twice one of the 2 cats got sick. The estimate for one cat was $3700 for a couple days and I could not get approved for that amount, so they put her down. Another friend had her cat need surgery and it cost her also somewhere around $3500, later it cost another $500.
My point is that now that I have no cats, I will not get another one because I am not rich enough to pay for the worst case scenerio, even though I see those heartbreaking ads on tv to go adopt a cat or dog that needs a home. Since animal pet insurance also does not cover pre-existing conditions, insurance is really no "insurance" that nothing bad will happen either.
But with bettas, I can pay for the worst case scenerio. Now, if you're a high school or middle school kid and your parents aren't exactly "animal people", then maybe one betta and one aquarium kit with a heater and meds and food should definitely be your limit, unless you have a job for your hobby.
Sorry for the long-winded response!
By the way, if I ever move I would love to give away some betta things to young people who know how to take care of a betta but maybe don't have funds. Wonder how I could do that locally?
Also - should people get another betta if they can't give it a full 5 gallon tank or more? Or is it ok to get another one and give it less, considering that so many bettas probably don't ever get adopted?