The shield isn't pure elemental Vibranium. It's a Steel/Vibranium alloy made using an unreproducible process. (For instance, Diamond and Graphite are both pure elemental Carbon, they trade, at vastly different prices.) Given that it is the only one in existence it could be worth a lot more or less until one can figure out how to reproduce it. From an Economic standpoint the price is set at whatever Captain will sell it for. There is likely no amount of money he would take for the shield. On the other hand, he would likely give up the shield if you could construct a hostage situation dire enough. This gets into the value of life. It's plausible you could get Captain to trade his shield for one innocent human life (~$5.5million).
Cost of raw materials.
0% Steel, 100% Vibranium = 5,443.10844 * $10,000 = $54.43 Million
100% Steel, 0% Vibranium = 5,443.10844 * $0.000255374 $ = $1.39
We know the shield is three times lighter than steel. Such a huge difference in density implies the shield has a very unique molecular structure implying a complex fabrication process (likely something more like Buckminsterfullerene which would explain the exceptional resistance to vibration and impact.)
Furthermore, it was made using an unknown catalyst during a WWII munitions program. Assuming the program cost less than the Manhattan project ($2 billion) it seems reasonable that one could recreate the shield for less than that - giving the shield and the knowledge of how to create it an upper value of $2 billion. Attempts by Jebidiah to do just that by capturing MacLain were not fruitful.
In an alternative calculation, we know Captain America was able to get a new shield from the Beyonder. You could calculate the cost of that mission and set a different upper bound. This is probably greater than $2 billion. We know that Dr. MacLain was unable to make more of the alloy but he was able to learn how to make Adamantium. This itself is a regulated good with a controlled price but could be used to calculate the cost of an inferior replacement (say 80% of the value of the original shield) if we could find the price of Adamantium.
Let's say we wanted to take an Insurance Policy on Cap's Shield. You would likely deal with an actuary who works in Fine Art. He would sit the Cap down, ask a few telling questions about how much he would sell it for, how many lives he would trade it for, how long he would work to make another, how often he expects it to see combat and create an excel engine to get a better picture of what Captain America's premiums.