I checked Digi-Key through RPiLocator and they report several thousand units in stock each of the Raspberry Pi 4 2GB at $45 and of the Raspberry Pi 3B+ 1GB at $35: https://rpilocator.com/?vendor=digikeyus

For those unfamiliar with them, Digi-Key is a electronic components supplier to manufacturers but they also sell to individuals. Their stock count should be accurate.