Inflation is not the only way to calculate the relative 'cost' of Greenland. I think a more accurate perspective would be calculate the offer in terms (a percentage) of GDP.
American GDP in 1946 was $228M [1] (in 1940 it was $100M). The USA essentially offered half of their GDP for Greenland.
American GDP in 2016 was $18,625M.
So in relative terms, the Americans offered roughly $9Trillion.
I could not find the information directly, but I found some historical figures for GDP[1]
The figures I quoted above are in 1946 USD.
The figures quoted in the spreadsheet referenced are in "million 1990 International Geary-Khamis dollars" (IGKD)
So the spreadsheet in 1946:
USA: $1,305,357 IGKD
Den: $23,690 IGKD
So Denmark's GDP was 1.8148% of the USA's.
Or in reference to the USA's GDP of 1946 being $228M, Denmark's was merely $4.14M.
$100M in 1946 would have been a staggering amount of money, especially in the context and aftermath of WWII. It should also be noted that Denmark was largely untouched by the war, and in 1946 their economy resumed prewar output. This is probably what the leading factor was in turning down the purchase offer, and I generally agree that it was the right decision.
You've misinterpreted that. It's not 0.228 billion, it's 0.228 trillion ('t'), as in, $228 billion. The US couldn't've possibly been as poor as $228M GDP. (It grew fast after WWII but not that fast!) It is still, however, an extremely large amount of money either as a percentage of GDP or government budget.
American GDP in 1946 was $228M [1] (in 1940 it was $100M). The USA essentially offered half of their GDP for Greenland.
American GDP in 2016 was $18,625M.
So in relative terms, the Americans offered roughly $9Trillion.
[1] https://www.thebalance.com/us-gdp-by-year-3305543