Great question! I wish I had a more realistic idea before I got started. It has been a lot more than I expected and I only have a 30 gallon. And actually I wish I had gotten a 55g. Definitely get the biggest tank you can afford! I have spent $450 so far and I am sure this is on the low end because I bought some used equipment and as many sales and bargains as humanly possible! It's been worth it though because I am now one of the "obsessed"! Here's a run down of what I have bought to give you and others on a budget an idea of what to expect:
I have a fish only with live rock and hardy inverts.
$26 book "The Conscientious Marine Aquarist" - online
$80 30 gallon tank, hood, and stand, used heater and hang on power filter - used
$130 18 lbs live rock, 15 lbs salt mix, amquel, stresszyme, ro water - from local fish store
$95 1 raw shrimp, 10 gallon qt tank w/ hood and light, 50 lbs aragonite sand,2 thermometers,heater for qt,2 backgrounds, power head for qt, 2 algae scrubbers, 2 nets, 2 pieces pvc pipe, timer, multi outlet, buckets and lids for water, tubing scrubbers, tubing, hydrometer, turkey baster, test kits, fish food - from local pet store and walmart
$65 power head, heater, power filter for 30 g - online
$40 15 various hermit crabs, 1 turbo snail - lfs
$11 2 fish - free molly from lfs and nemo fish on sale for 10.99!
So as you can see the fish are the least of your expenses starting out! PLUS I still need the following:
$45 large bucket salt mix
$25+ more snails and a few more crabs
$90+ reverse osmosis unit for home use
$100+ Protein skimmer
$60+ more live rock
$15 replacement filter cartridges
$12 ground fault interrupter
$20 power head for water bucket
total here = $367
$?? More fish eventually
$?? sump/refuge eventually
$?? better lights/hood for corals/anemones eventually
$?? Bigger tank eventually
So you can see how it gets really expensive really fast. I will have $1000 in this 30 gallon fowlr with 10g qt before it is all over. And I am very cheap, believe me. But I love it and would do it over again!
:happyfish