Your $750 as the "true cost" is just a construct for your own estimations of value. The other factors of convenience of retail buying (includes customer service) or convenience of wholesale selling (always buying) are also factors that can be tallied, given dollar value and entered in your books as "cost of sales" or a one-time write-down. But if hoverboards sweep the markets, the value in bicycles could plummet, just as a huge gasoline crisis could make bikes highly desirable.

From the viewpoint of Ayn Rand's Objectivism, we too easily say that value is "subjective." Value is not arbitrary, even though different people can objectively evaluate something differently depending on their own personal (but objective) values. My daughter is long grown up, so children's toys have little value to me. If a parent makes evaluations among them, that is also objective for them, based on their (personal) values. But neither case is subjective in the sense of being arbitrary or non-judgmental.

I am not sure that belaboring the specifics of the numismatic markets provides more general understanding. The fact is that for 70 years, the value of silver was so low, that at a parity of $1.2929 per ounce, silver coins were worth more as tokens, at first (until 1933) against gold, but even later against paper dollars. Once silver crossed that line, it became profitable to hoard, sell, and melt common silver coins. But we are talking of prices still under $2 per ounce, then $3 per ounce, then $5... Over about ten years, millions of Washington Quarters and Roosevelt Dimes were (slowly) turned back into bullion. And silver was still coming from secondary smelting of copper and recovery from film processing.

Then Nelson and Bunker Hunt decided to corner the silver market. They took actual physical delivery from the silver futures exchanges. (Futures markets are intended for producers and consumers to nominalize supply. Farmers wheat co-ops buy and sell wheat futures against the cash price. That prevents spikes immediately before harvest and drops immediately after.) Silver skyrocketed to $50 per ounce in a few months. Against that, the marginal numismatic value in a Proof quarter was negligible.

Also at play - and unpopular in places like this - was what Keynes called "the animal spirits." Coin dealers who eked out a living suddenly saw huge cash influxes. Everyone who knew the Tulip Craze knew that it would not last, so they made the fastest money they could the easiest way possible. It was rational, given the market conditions. Again, in year 1, a silver dollar with 75 cents of silver in it for sale as a rarity for $2 now in year 9 has $40 dollars of silver in it.

Another example involves gold. Today, with gold at $1300, you cannot touch a $3 gold piece with $200 of gold in it for less than $750. Back in 1935, they sold for a small margin over bullion, along with $10 and $5 and $20 gold coins. Today, we know that the $3 are objectively rare because numismatists did more research and reporting from Mint records.