I'm a fellow FNG, so I can't offer too much sound advice, but here's a good thread to read . . .
https://www.saltwaterfish.com/vb/showthread.php?t=235658
A good "What do I need?" read.
Also advisable to pick up some good paper reading material such as
The Conscientious Marine Aquarist (Fenner) and maybe The Simple Guide to Marine Aquariums (Kurtz), both available from this site. While Fenner's book is considered the "Bible", I believe it's a few years old and a lot of the (Very good I might add) advice you'll get here may be in contridiction . . . so many different approaches, I've found there's few real "Silver bullets" when it comes to what to do.
As for cost, there's no getting around that this is an expensive hobby, although there are ways to mitigate cost with DIY techniques, and judicious shopping. As an example, so far I've acquired a 90g AGA tank (w/overflows, stand and basic cover), a MegaFlow 3 sump filter, four heaters (two for the tank, one for the quarantine tank, one for mixing saltwater), a pump for sump, a couple of powerheads, and a Coralife PC light system that will allow for some inverts in the future . . . hit to the wallet has been around $1200 (Including tax). That's all after a lot of shopping around and I feel I've gotten pretty much the better deals around, and that's not even counting the few hundred I spent just today to have quad grounded outlets installed by my tank (Our older house has an ungrounded electric system and figured the heavy power load might strain the system, not to mention the significant safety issue to us, the tank, and the house itself). Once the cost of live rock, a skimmer, testing kits, and an RO/DI water unit, and some other odds-and-ends are added, I'm looking at around another grand I figure.