Thanks Bill. This calculator
https://www.bls.gov/data/inflation_calculator.htm
estimates that $49.85 in 1959 equates to $424 today. Expressed as a yearly inflation rate that is roughly 3.8% a year.
Assuming the pistols sold in that ad were military P08s in average condition and original finish, applying various annual average appreciation rates to that $49.85 original cost:
5% per year =$ 845
6% per year =$1,460
The way you read this is "if the pistol went up an average of 5% per year from 1959 to 2017, it is worth $845 today".
So, from 1959 to now, based on the assumptions stated, my guess is that this hypothetical "average" pistol would today be worth at least $1,000, i.e. it increased in value roughly 5%-6% per year. Phrased differently this would seem to support the idea that Lugers appreciate at a couple percent a year above inflation.
Thanks for posting that ad, the only way to figure out appreciation rates is to know what they sold for at earlier dates.