Very little.
I have bought used chains, often for $1 per loop (or less).
Unless sorted by pitch, gauge, drive link count, and brand.
Then a little more.
If sharpened, and in really good shape, with the original box: a little more. If the buyer has to sort, clean, repair, and sharpen: less.
With mail order and Internet sites, you are competing with sale prices on new chains, plus shipping costs.
You can look through the Trading Post and see what other members have asked.
Philbert