I am interested in finding out as much information as possible about
an Italy string/violin maker - "Andrea S Postacchini " during 1830 to
1860. I also want to find out, if possible, the histrical selling
price of the violins made by him.(e.g. auction date/price, ...etc.)

Hello rick888:

Thanks for the interesting question!

I was able to find out some good information about Andrea Postacchini.
The following are the best sites I found. I've pulled quotes from each
site, but I suggest you read through the entire articles.


Andrea Postacchini - Italian Violin Maker 
URL: http://www.maestronet.com/m_library/maestro_mag/Andrea_Postacchini.cfm
Quote: "The Italian maker Andrea Postacchini is often referred to as
the "Stradivari of the Marches". Although Postacchini is the most
famous violinmaker to come out of this region, until now little has
been known about him, with much of his output being credited to
another Andrea Postacchini, due to the variation in style and
refinement between his early and late work.
According to the archives in the Santa Maria delle Vergini church in
Fermo, there was only one Andrea Postacchini and he was born on 30
December 1786 in Fermo, a hilltop town near the east coast in Italy's
marches region. Postacchini spent his life in Fermo and died there on
3 February 1862, age 76."
Note: Excellent biography!

The Sixth International Musical Olympus Festival
URL: http://www.musicalolympus.spb.ru/eng/musolymp/fest2001_print.html
Quote: "Soloist, Ilya Kozlov (Russia), First Prize and Grand Prix, The
International Andrea Postacchini Competition, Italy, 2000"
Note: Apparently, there is a world-class violin contest named in his
honor.

Lucina Horner
URL: http://www.alabamasymphony.org/musicians-horner.html
Quote: "Lucina plays an old Italian viola, made by Andreas Postacchini
in 1832."
Note: He made violas too!

ANDREA POSTACCHINI - Lo Stradivari delle Marche 
URL: http://81.72.160.202/corriereproposte/index.php/article/articleview/1708/1/18/
[in Italian]
URL: http://translate.google.com/translate?hl=en&sl=it&u=http://81.72.160.202/corriereproposte/index.php/article/articleview/1708/1/18/&prev=/search%3Fq%3DAndrea%2BPostacchini%2B%26hl%3Den%26lr%3D%26ie%3DUTF-8
[translated by Google to English]


As for the value of his violins: 

Auction Highlights
URL: http://www.stringsmagazine.com/issues/strings96/Auction.html
Quote: "POSTACCHINI, ANDREA [SK5/41] Italian Violin w/case ... $17,250
£11,994"
http://www.stringsmagazine.com/issues/strings93/Auction.shtml
Quote: "POSTACCHINI, ANDREA (attributed to) [S1114/41] Violin w/case:
Italy, mid 19th C. ... $20,449 £14,300"

Violins for sale - over £5000
URL: http://www.aviolin.com/violinsover5000.html
Quote: "Andrea Postacchini, 1824  £25,000" 


There are many pages in other languages as well, if you do the
searches listed below. :-)


I hope this information helps with your research. 
                          
If you need any clarification of the information I have provided,
please ask using the clarification feature and provide me with
additional details as to what you are looking for. As well, please
allow me to provide you with clarification(s) *before* you rate this
answer.
                          
Thank you.                           
                          
websearcher-ga                           
                                            
   
Search Strategy (on Google):  
   
Andrea Postacchini
Postacchini violin

All it take is one request to get what I really need. Very impressive !