Thanks to the wonderful Chronicling America online newspaper database at the Library of Congress, we can discover a time in American history when marbles cost but a few pennies. Some of these same marbles today in mint condition could fetch hundreds, even thousands of dollars.
For instance, this advertisement from Kress' 5-10 and 25-cent store on page 5 of the February 10, 1907 Pensacola journal details a price list:
Yes, that's 20 German swirls for 5 cents. Klondykes, according to the German marble posters I have seen from that period, were onionskin marbles (possibly containing lutz). Note how real Carnelian agates, prized as shooters, cost as much as big sulphide figure marbles. 5 cents could get you 75 polished clay commies.
Despite the vastness of this collection, I found very few detailed advertisements like the above. By and large marbles were mentioned generically among other toys. I'm sure someone with more time on their hands, and more creative advanced searches, could dig up more interesting tidbits.