Just brainstorming a little ...
At some point, U.S. CuNi nickels might trade similarly to the way copper cents do now.
If my math is correct, $310 face in nickels (assuming no wear) would weigh 31kg (about 68.34 pounds).
Medium flat rate shipping costs $12.35.
For a buyer to pay 6 cents per nickel (shipped) would cost $372.
That would leave about $50 for the seller for his time/effort/supplies/fees/etc. I think once the coinflation value of the nickel gets to 7-cents or more, there might be some trading going on.
I bet if someone put a buy-it-now for $399 on eBay for a "Nickel CTU" with a good sales pitch, he could probably make an occasional sale even now.
Ah, probably still isn't worth it. What would the eBay+PayPal fees be on $399? I haven't sold on eBay since 2002.