Hi, I'm a newbie myself, so don't take my word for everything perfectly, but i can tell you what i've read, been told and am doing on my own tank. for starters you can have a tank as small as 10g (though not recommended). Most recommend you start with 30g minimum (this is what i have started with). Obviously the bigger the better in terms of about of future work. Easier to maintain as it is less likely that you will see huge changes in chemistry balance of your tank. Therefore you may need to make less water changes or not as often. Also the bigger the tank, the more fish and more variety of fish, as you won't be able to put certain fish in small tanks due to size. Next you have to decide, if you want FO,
FOWLR, or coral tank. i spent a little over 150 to get my tank started, but that does not include any live rock or fish. that is just the purchase of the tank with lighting, sand, salt, good testing kit, filter, heater,
hydrometer and a few other things. with the purchase of my first 2 fish i'm looking at 200+. Also it's wise to get live rock, which is really expensive. I miscalculated that and now don't have live rock, though i hope to fix that in the next few months. i would say you are looking at closer to 250 to start.
I wanted to add that basic lighting is fine for FO tank, but as soon as you plan to add Live rock and more importantly corals, you have to upgrade your lighting which can cost you big bucks. also if you have a 30g tank, and FO or FOWLR you might not need a skimmer if you do routine water changes. as soon as you get coral you will need a skimmer and that will also cost you over $100.