Ditto on buying a big tank. A lot of fish (tangs, angels, mandarinfish, pipefish, eels, etc.) need at least a 150 gallon tank. Or if you want to keep multiples of the same species, you need a very large tank with plenty of caves, tunnels, and rockwork so they don't kill each other. Most saltwater fish are jerks and enjoy nothing more than tearing each other's fins apart, or forcing their victims to jump out of the tank. Speaking of which you ABSOLUTELY NEED a tight fitting lid for the tank. You can also buy special mesh and frames for reef tanks to go over the top of your tank (again, don't just DIY something since it can severely impact the PAR of any light that passes through it; you don't have to worry if you aren't going to keep coral). A few months back my convict chased three clownfish out of the tank, DESPITE IT BEING COVERED, before we rectified the situation. Stressed fish will jump through even the smallest of gaps in the cover in order to escape an aggressor.
Anyways, you'll probably want to go with fairly docile fish, with decent lifespans, who stay relatively small, and are captive-bred (no matter how much research you do, you will never be prepared to try to get a will-caught marine fish to eat. Heck, it's hard to teach captive-bred fish to eat, unless they were bred by ORA). So, what fish probably aren't a good idea? Here:
Pipefish (require live food and a species tank)
Seahorses (require live food and a species tank)
Mandarinfish (eat a ton,require multiple feedings throughout the day, are very shy feeders, and require live food unless obtained from ORA)
Angelfish (aggressive, mostly wild-caught, need large tanks, often eat coral, and need to have sponges in their diet to ensure proper digestive health and behaviour and a long life)
Yellow tangs (I'd only really recommend captive-bred blue tangs or captive-bred/sea pen raised convict tangs; all other tangs are either massive, aggressive, too active, are harvested unsustainably/using cruel methods)
Damselfish (they may be small, and they may live in groups in the wild, but they're bloodthirsty little psychos in captivity)
Butterflyfish (very few survive capture and quarantine; over 90% end up dying)
Any large predator (lionfish, groupers, etc.)
Wrasse
Dottybacks (they can be extremely territorial and aggressive)
Really, the only beginner fish I'd recommend are (all of these are available captive-bred; make sure the individual you are buying is captive-bred before purchasing):
Ocellaris clownfish (live a long time, don't require much room, eat well, docile unless threatened; can be kept in a nano)
Skunk clownfish (same as Ocellaris, except they're far more timid and docile and are easily bullied to death by other fish; can be kept in a nano)
Pyjama cardinalfish (inactive, can be kept in a school)
Banggai cardinalfish (only buy captive-bred ones, and be aware that they often carry the 100% fatal Banggai cardinalfish iridovirus; don't require much space, inactive)
Striped blenny or mimic blenny (they have amazing personalities, eat well, are very gentle, and are highly interactive)
Chalk bass (only available as wild-caught, so I'd wait until they're available captive-bred seeing as over 80% of wild-caught fish die before making it to your tank)
Blue tang (I'd recommend at LEAST a 5' long tank since they're very active; among tangs, they are one of the least aggressive, but they're also fairly anxious fish)
Convict tang (can actually fit fairly comfortably in a 100 gallon tank; less aggressive than most tangs)
Nearly any captive-bred goby (cute, tiny, good for nano tanks; they have short lifespans, so you need to replace them every few years which increases the risk of infecting your tank; watchman gobies have a decent lifespan)
Oh, as for cost? Assume everything's gonna cost AT LEAST $10,000 in total. Don't try to cut costs, since you'll just end up spending extra money to solve problems caused by trying to be thrifty.
