This is not so easy. See http://en.wikipedia.org/wiki/Reichsthaler
Consider 1000 Reichsthaler: What were they worth in Breslau, 1825-1827, and today?
Perhaps this linked calculator for 'Kaufkraft' (purchasing power) is sufficient for a rough estimate: 'Kaufkraft als Massstab fuer den Wert des Geldes' (Purchasing power as a scale for money's worth)
The red 'Kaufkraftrechner' (calculator as in calculating machines ...) has a lower register which shows the following results:
1 Reichstaler = 3 Mark (historical risky relation, but I have no other possibility for the moment) That would mean: 1000 Reichsthaler = 3000 Mark
Now click on the 'Kaufkraftrechner': upper window: fill in 3000 Mark and calculate ('Kaufwert berechnen')
1) 1794-1818 (~the time Mendel was conceiving the bequest; also ~Napoleon's time): For 2012 this will give in the lower window 48'779,61 Euro
2) 1819-1838 (~the time of the file's date,1825-1827): For 2012 this will give in the lower window 58'160,30 Euro
So it is reasonable to estimate a current equivalent of, say, 50,000 Euro, this having no pretentions to being any more than the roughest informed guess.
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