OK, I am very suspicious of this - one can "harden" living items by a variety of means, and I take it from your description that these look "just like" ginger & garlic, not like they had been buried or encrusted in some form. To test if they are naturally formed I would have to see them in the context of their discovery - that is, where they were collected. It might be possible to determine if they were faked if I could sample them chemically or possibly if I could section them to see the cell structure. Similarly, I could look at them to see if they showed any signs of burial. A really quick (but not conclusive) test would be if they still retained any odor - if they did, they are certainly not fossil. Lastly, we could try a Carbon 14 date on them - if they are older than 50,000 years it will tell us nothing. If they are younger, it could give us an age - right down to demonstrating they were alive last year.

As to age, a fossil is any evidence of pre-existing, pre-historical life so they could range from 10,000 to millions of years - again, I would need to see the context of their discovery to tell - assuming they are truly fossil.

Value is in the eye of the beholder - but good fossils of recognizable objects are dependent upon common-ness or rarity. If he has just 2 of these, the price is way low. If he has 200 - then maybe $8.00 is right.

Ginger fossils have been recognized from foliage and fruits starting in the latest Cretaceous through the Miocene at least. Go to
fossil
and type in Zingiberaceae for the search term for an example. I am unaware of any fossils of Allium.

Finally, as to the SEM - Its great power is in resolving small three-dimensional structures. Thus the real question is, what interesting questions of nature can you envision for which such information would be useful? In my own field (Botany) the SEM is very useful to understand the structure of the surface cells of leaves, or the identifying characteristics of small fruits or seeds. These data can be applied to systematic problems (determining species), but also to archeological ones (what did people eat & discard around hearths of long ago?)