Soon after I got my first DSLR, a D50 in 2006, I got a hankering for some new lenses. I had several old film lenses, including a Nikkor 20mm f4 K, Nikkor-S 35mm f2.8 and Nikkor 85mm f1.8 K -- but only the 20mm would fit on the D50, and for a long time, that was my widest lens. Then I answered an ad for some Nikon film gear, and for $120 I came away with a Nikon F with Photomic and plain prisms, a 135mm f3.5 AI, Micro Nikkor 55mm 2.8 AIS and 50mm f1.2 AI. I sold the Nikon F body and its prisms for twice as much as I had paid, and just sold the 50mm after years of use -- great lens. I still have the 135mm and 55mm and won't ever give them up.
Since then, I've gotten other Nikkors for "free" -- if you don't count the time spent wheeling and dealing.