It was not so very long ago that animal pelts could be used to pay debts, purchase
food and other things. The term "buck" meaning a dollar is still used frequently.
Not clear what a doe sking was worth. From the Internet:

"As the preferred slang term for what Washington Irving called
"the almighty dollar," buck in all likelihood sprang from buck
skin or buck hide -- a commodity of exchange, and
metaphorically a loose measure of value, in Colonial trade with
Native Americans. ("He has been robbed of the value of 300
Bucks, & you all know by whom" -- this 1748 quotation comes
from the Ohio River Valley, and is cited in Mitford M.
Mathews's A Dictionary of Americanisms.) The earliest
undisputed example of buck in the precise sense of "dollar"
("mulcted for the sum of twenty bucks") has a Sacramento
provenance, and dates back only to Gold Rush times. Although
the Forty-niners may well have popularized this new sense,
traders at outposts east of the Continental Divide were probably
already using it; the scanty written records of vernacular speech
of the time preclude certainty. Unlisted in early slang
dictionaries, buck seems not to have gained national popularity
until the 1890s -- a good example of the slow dissemination of
slang in the days before radio, television, and the Internet."