Nikon F - 46.5mm
Pentax K and m42 - 45.46mm
Leica R - 47.0mm
Olympus OM - 46.0mm
Canon FD/FL - 42.0mm
ConYash - 45.5mm
Minolta SR - 43.5mm
I think most people would be GLAD that Nikon lenses hold values reasonably well. Buy an old fully depreciated Nikkor for 35 to 50 dollars and you will likely be able to sell it for just about the same.
Buy a body for 10 dollars and it makes no sense to sell it because you can get so little and not worth the trouble.
I think this is a non-issue.
Look on the bright side, if the body is so cheap then that frees the extra dollars for the Nikkors. Ten dollars for a body and say 50 for a lens, $60.00 is an absolute bargain for such a quality shooter. I do have a non Nikkor 50, or 58 actually, and it is the 58mm 1.4 Auto Topcor which is the Topcor tribute built by Cosina in AIs mount. Not cheap though, but superb in every way.
Hang on, are truly complaining at $35 for a working 50ish mm Nikkor? Given the quality $35 is a gift
Why hack a lens when there are adapters all over the bay to put various lenses on Nikon bodies. You may need an adapter with a lens but you can still do it. Of course with the advent of mirrorless, the old Nikon lenses are just as popular today although deals are still available.
Things are worth what they are worth, and $20 to $35 is what I expect to pay for a normal lens around f/2 in good shape from any major camera maker, though I might get one for less (and for some lenses, more). At any rate, the price of a normal lens in a long-abandoned mount of limited current popularity is not relevant to the price of a normal lens in a still-current mount of high popularity.
When new, a Nikkor f/2 was probably around 25% the price of a new Nikkormat, maybe a little less. So, to extend your logic regarding a camera body/normal lens cost ratio, a good used f/2 Nikkor should be around $2.50, which isn't realistic.
Besides, how in the world is it going to be worth it to convert a lens to Nikon mount, losing auto diaphragm function, when the most you can save is $35, and that's if the lens to be modified is free?
Well, telling comments!
To those of you who say or infer that ALL normal lenses are in the $30 range today, I say NO!!! Normal Minolta MD or MC lenses as well as M42 and Konica and Yashica bayonet ones can be had for about 1/4 the price of a normal pre-AI Nikon lens. Canon normals and Pentax K normals can be had for about 1/2 the Nikon ones or less. Sorry, that is what I experience in the Philadelphia region.
Why don't I simply avoid the Nikon bodies? Because the temptation is too strong with prices so low. About a year ago I bought eight Nikkormats for less than $100. They need lenses. 28mm and 135mm aftermarkets are NOT a problem. You see, I want to have my cake and EAT it too: dirty rotten spoiled, I am. And, somehow, someway, I WILL GET a bunch of normal Nikons and not spend much. Few know how persistent I can be in my enduring quest for frugality. But I wanted some feedback and I got it. Thank you all.
As far as the most seemingly sensible answer "get a mount allowing M42s": we (most) already know that that 'solution' demands another lens element being introduced into the equation because Nikon bodies are so 'thick' (46.5mm distance between mount and film plane). I am sufficiently 'purist' to not allow that 'optical ignominy' to happen. - David Lyga
Off-brand Nikon mount variable aperture normal zooms from the early 90's. Problem solved.