Jumping in real quick because I have a bit of a horror story about this. I tried to find a cheap Dior Addict glow for my cousin last year on one of those random discount sites... honestly, it was a disaster. The packaging looked okay but the actual lipstick was super waxy and smelled like chemicals. Be really careful because luxury brands like Chanel and Dior basically never go on sale at places like Macys or Nordstrom. They control their pricing so strictly that if you find a brand new one for half price, it is almost certainly a knockoff from a factory that doesnt follow safety rules. If you're really tight on cash but want the real deal, I would suggest looking at this luxury outlet just to see if they have any overstock, but even then, it is risky with your Saturday deadline. Another thing to consider is that 45 dollars is basically the exact price for one. If you go to a real counter, they usually give you a nice branded bag and some tiny samples for free which makes the gift look way more expensive and fancy than it actually was. Just make sure to check the batch code on the bottom of the box if you do find a deal elsewhere to make sure it isnt five years old and expired. TL;DR: Be super cautious of deep discounts because fakes are everywhere and can cause nasty skin reactions. Luxury brands rarely mark down, so your 45 dollars is best spent at a legit counter where you get the fancy packaging for free.

TL;DR: Sephora. I bought a Dior lipstick for exactly $45 last week. Its tight with tax but definitely the fastest way to get one by Saturday.