Hi Dénes,
if I remember correctly, there are figures for Bf109-costs for the Erla-Factory stated in "Sachsenflug und Messecharter" (by Peter Kühne and Karsten Stölzel, ISBN 3-928833-41-3. See for example
http://www.cvb.de/Verlag/regionalia.html
- scroll down to about two thirds of the page).
Unfortunately I have no access to my copy for the next weeks. Therefore I´m not able to verify wether these are production-costs or prices paid per example. Also I´m not able to give their sources. Perhaps some other member is able to?
This is a nice book on the general aviation history in Leipzig. It only contains about five pages mentioning the Erla-Works rather generally, so it might not be woth the price, if you are interested only in Bf109-related information. Otherwise it´s a nice and interesting book!
Greetings
Ralph