Nikon's early AF 300mm f/2.8 — body-driven screw AF version before the AF-S upgrade.
The Nikon AF Nikkor 300mm f/2.8 IF ED is the original body-drive AF version of Nikon's professional 300mm — predating the AF-S versions. Body-driven screw AF via camera motor. ED glass for excellent optics.
Optically good — ED glass provides quality at 300mm f/2.8. The body-driven AF is slower and louder than later AF-S versions. IF internal focus keeps barrel constant. The f/2.8 at 300mm provides professional reach.
Nikon F mount with 39mm drop-in filter holder. Body-driven AF — speed depends on camera motor. Heavy — professional super-telephoto. No VR. ED glass. IF internal focus.
Available used very cheaply — the AF-S VR versions are dramatically better. Body-drive AF limits speed. For absolute budget 300mm f/2.8 on bodies with AF motor. Check for smooth AF operation.