Tbf I had envisaged getting a massive tank once I'd moved and got settled in but the estimated running costs are eye watering. When I do come to get one again, they really help with my mood, I'm going to have to be much more conservative
Running tanks doesn't have to be expensive.
These days I'm running four (2/4/4/6-footers), until around the pandemic starting I was running six, including a 5-footer in the garage. I should really move my African Butterfly Fish in with my old Leopard Bushfish, to decommission the 2-footer!
Over the past 14 years, I've only run heaters during the most bitter winters, with the exception of when some of my African riverine fish were in the garage tank.
Most of my fish over that time have been "tropical," but I have had some temperate species. My indoor tanks have very rarely dropped under 18C and have hit 31C in summer heatwaves.
The one big tank I bought new has proper lights (2* 110W?) on ~6 hours per day for the benefit of the Anubias plants (using 14 year old original tubes), another 4-footer has the lid/light from my 2-footer (15W?) for ~5 hours per day as it's often in the shade.
Most of my active filters these days are Fluval U4s and an (Eheim?) hang-on-back for the 2-footer, these are all very low Wattage filters, maybe ~15W each.