Staple Cheapies and Must Haves

Enthusiastic newbie here trying to put together a small collection without going broke. I have noticed that there are several go to perfumes and oils mentioned in this sub that are surprisingly cheap. I have already picked up Nemat Amber Oil, and Im looking at getting the Vanilla Musk too as well as the Al Rahab Choco Musk. Im amazed they're all under $20 so I figure I should ask the community what others Im potentially missing.

What are your staple and must have items in your collection that can be picked up for under $20?