Those prices didn't change much until after the mid 1960's.
You're right. From 1951 to 1959 the 99 models increased only about $2.
By the mid-60's, the 99E was at $105, 99F/99C/99DL from $134 to $141.
Prices jumped almost 20% in the late 60's.
The 70's saw the prices almost double.
In the 80's prices doubled again.
