cripes, this is probably not something I want to add up. started my first tank in 1998, 30 gallon tank, while in college. From there a 58 gallon after graduation, a nice 150 gallon build in my first house, and then a 300 gallon tank I've had for the last 12 years in this house. I'd say an average of $2k a year on sustaining (electricity, salt, food, filters, etc.), probably another $1500 a year in equipment upgrades, adding fish/coral, etc. I'm easily in $70k over the last 20+ years. BUT.. we're allergic to dogs/cats, and so when I see what my folks or friends spend on their pets, for me it's an easy trade. I've loved the hobby, so I don't really make decisions on cost (it's a factor, but not the primary one).