500 chickens

Rogue: I have ten gold pieces. How many chickens can I buy with that?

DM: Well, at 2 copper each… 500.

Rogue: I’ll buy 500 chickens, then.

DM: But the farmer selling them only has, uh, 31, so that’s your limit. Besides, how would you even carry them?

Rogue: How much would enough string to tie 31 chickens together cost?