The cost difference is very significant.
Nikon 35-70mm f/2.8
Nikon 80-200mm f/2.8 D ED
Example Image shot using the Nikon 35-70mm f/2.8 D
What You’re Not Getting With Legacy Nikon Lenses
Things to Watch Out For
Lens Fungus – Is a microbial growth on the lens surface. In some cases the fungus can be cleaned and the lens restored, in others the fungus can etch the coatings and glass rendering the lens unusable.
Cloudy or Hazy Lens – More than probably it is fungus and the lens should be avoided if you are purchasing.
Separation (balsam separation)-The elements in lens are typically two separate pieces of glass which are cemented together. After a long while (usually 20-50 years) the cement breaks down and fails causing the lens elements to separate.
Scratches – Older lenses that have not been well cared for can have scratches typically on the front element. These will have an effect on image quality and should be avoided.
When looking for lenses online the seller (if they are being open and honest) will shine light through the lens and take photographs to show the condition of the lens. Most will also include the serial number which is also very handy in determining exactly which variant of a particular lens you are looking at. If you are considering the purchase of an older lens it is a good idea to ask the seller directly if they checked the lens elements for fungus and separation. Another very informative and handy site has the serial number ranges and specifications for pretty much all Nikon lenses that were ever built. Here is the link to it. Another site (AllPhotoLenses) has a user supported database of a very large number of lenses by all manufacturers. The link to their site is located here.