I have no clue, but for my current setups(listed in my current tanks section) I have spent more than 15K in 2 years and if you include power, etc., I'm looking upwards of 20K. I have serious addiction problems and need to stop trying to get ALL the cool things. Bear in mind, this is for six tanks and a whole bunch of other things I have still yet to get around to, including a 180G, and a bunch of tanks ranging from 20-40G each.
I will tell you, I have calmed down significantly now that I am almost out of room. I would say on average, maybe 300-500 each month including utilities increase, or 100-300 on corals, fish, foods, buffers, equipment, etc.