They in this sentence refers to:
"worked leather cowboy boots studded with silver conches".
What does the phrase in the topic mean? The boots could sell for 6 times as much now because of the silver?
EDIT: I don't seem to have enough to comment on the commentators below, so I will ask my follow-up here.
Does this mean the last part of the sentence
"...if they went for a quarter"
only serves to clarify the unit mentioned in the beginning (in this case, money) and not about any cost (a quarter)?