The original German name may have been spelled Kühborn. The umlaut (ü) is very close to "i" (pronounced eeh). This means you should look to finding the names Kühborn or Kiborn.
When you look on the Radix surname list of old Hungary, there is one Kiborn in the trade and industry list (which was like a yellow pages). This Kiborn lived in Nagy Gaj in old Torontál county in the Banate region. It might be worth the fee to the Radix databases to find more detail about this Kiborn.
The Ellisisland database also has just one Kiborn. His first name was Frank and he went to Toronto.
The town name you have from the letter may have been Csösztelek. This town had the German name Neuhatzfeld and was in old Torontál county. It was not in the same district as Nagy Gaj, but not too far either.
You need to connect with web sites for the Donauschwaben and Banatdeutschen. Look for the name in Zichyfalva near Nagy Gaj. Here is a website which had many Kühborn and one Kiborn: http://www.zichydorf.h-kaiser.de/Zichydorf/Familiendaten/SIB...