In absolute terms, prices of mid/late 1940´s don´t say too much. But when you compare them with prices by other brands or models, it´s quite interesting!
The Sea Hawk wasn´t that affordable then:
In 2003, $71.50 from 1947 is worth:
$589.31 using the Consumer Price Index
$490.06 using the GDP deflator
$1,057.56 using the unskilled wage
$1,595.56 using the GDP per capita
$3,212.29 using the relative share of GDP
In 1945, the average Annual Salary in the USA was about $2900; thus the pictured "De Luxe" Sea Hawk was 1/40 of this.
In Germany, the average annual salary was 26.700 Euro in 2003; a 1/40 of this equals 658 Euro. For comparison, the average price of a swiss watch was 329 Swiss Francs (roughly 220 Euro) in 2003 (from FHS.CH).
That may say watches became a lot more expensive since 60 years ago, which may be understandable if keeping in mind they are luxury objects today rather than a necessity in 1940´s.
And it may say GP watches ever since have been more precious than average; just that, unlike many other luxury brands today, GP didn´t do them as fine and precious back then as they do them today. But that might be apparent from the watches.
In terms of the Sea Hawk, it´s a real tradition for GP and the model line actually is much older than many enthusiasts know!