Originally Posted by ZergyMonster
The added costs to keeping fish is the monthly cost of electricity for running filters and/or heaters and lights.
I wouldn't truly consider the cost of electricity a concern most small internal filters only use a few watts of power and even a 25w or 50w heater isn't necessarily using much energy because they're not constantly on, but even if they were, that's only as much as a light bulb. Compared to the rest of the things contributing to your power bill, a betta or small fish tank is really not going to have much of an impact at all.
I tend to feel like food goes stale before I use it all up.. I buy more every few months and usually toss the old stuff but I've never emptied a container of fish food. Omega One is $3.99, Hakari is slightly less (but less volume). I have 3 bettas and they don't make much of a dent in their food. I could be cheap and keep the food until it runs out, which would "save" money, but since my average expense for pellet food is maybe $12 a year I'm okay with wasting some :)
Frozen foods (blood worms, brine shrimp, etc) are about $5 a package, but they actually keep a very long time (mine have expiration dates a couple of years in the future) - I did the math for my ADF (frogs) and just ONE package of frozen food is probably a year's supply for them.. Splitting them into portions for the bettas too it's still easily 6 month's worth. Having multiple options means I have a stockpile of frozen fish/frog food for a long, long time :)
Water conditioner is an initial expense, but a 100ml bottle of prime ($5.49 now at Petsmart) will last an average betta keeper (with a tank 5g or less) at least several years at 2 drops per gallon of water.
What DOES get expensive, is if your fish needs medication for any reason. I just spent $18 on Maracyn and Maracyn plus, and while I will have some left over, odds are good if I had to treat a fish again I'd have to buy more to complete the course.