The upkeep isnt the expensive part it's the initial investment. :-(
I also would say bigger is better as far as stability in the tank, BUT then your looking at higher start up costs.
Are you planning corals or just fish? If you are going just fish do you ever see yourself wanting corals? That will dictate your lighting and stock list.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.