Look, I totally get why you're stressed because that world feels super intimidating at first. 600 bucks is actually a decent chunk of change, but for a full "luxury" look including shoes and a bag, you gotta be a bit strategic. SSENSE and Mytheresa are 100% legit, so dont worry about them stealing your info, but their stuff can be pretty experimental and pricey even at 50% off. I would suggest checking these out instead:

• The Outnet Clearance Designer Gowns: This is basically the outlet for Net-a-Porter. You can find actual high-end designer stuff for like 70% off. Just be careful tho, because their clearance is often final sale. If it doesnt fit, you might be stuck with it, which is a nightmare when you're spending hundreds.
• Saks OFF 5TH Evening Wear Collection: This is way more approachable. They carry brands like Badgley Mischka or Mac Duggal which are perfect for a black tie optional NYC wedding. It feels less "avant-garde" than SSENSE and usually has better return policies for us folks in the US.
• Nordstrom Rack Formal Dresses: Seriously, dont sleep on the Rack. You can snag a gorgeous dress and then find some Sam Edelman Hazel Pointed Toe Pumps for under 100 bucks. It helps stretch that 600 way further. Sales usually start way before Friday, honestly sometimes as early as the first week of November. Make sure to double check those European sizes tho... a French 38 is definitely not an American 38! If you see something you love, maybe order two sizes and return one just to be safe.

I literally spent months obsessing over my first designer purchase for a gala so I totally feel your energy right now! It is such a rush when you find that perfect piece. One thing I learned the hard way is that European sizing is a total trip... you really gotta check the size charts for every single brand because a French 38 is not the same as an Italian 38. My first big win was finding a Marc Jacobs The Snapshot Crossbody Bag Saffiano Leather for way under retail by watching the clearance sections like a hawk. Quick tip: always look at the fabric composition! If you are spending hundreds, you want silk or high-quality wool, not just polyester. I once grabbed some Stuart Weitzman Nudistcurve 100 Sandal and they have lasted me through four weddings because the quality is just night and day compared to cheap heels. Also, dont forget that many sites like Saks Off 5th or Neiman Marcus Last Call start their private sales for members a week before Black Friday actually hits. Sign up for the newsletters now with a burner email so you get the early access codes! You can definitely do this under 600 if you grab a dress like the Alice + Olivia Delora Fitted Mock Neck Dress when it hits that 60 percent off mark. It is totally doable and you are gonna look amazing!

@Reply #2 - good point! Honestly the sizing is what almost ruined my first big purchase too. I remember being so excited for a dress I found on sale, but when it arrived, I could barely breathe in it and it was final sale. Huge mistake. If youre shopping online with a $600 budget, you really have to be cautious about those non-refundable deals. I would suggest checking out Farfetch or even Yoox... they are totally legit. You might want to consider something like the Adrianna Papell Beaded Mesh Gown because they look so expensive but often go on deep discount. For shoes, maybe look at Nine West Tatiana Pointy Toe Pumps instead of the high-end designers to save cash. I ended up getting a Coach Tabby Shoulder Bag 26 Polished Pebble Leather and it fits the vibe perfectly. Just make sure to double-check those measurements before you click buy... sales usually start way before Friday.