RFID passive tag reading upto 30 cm

hello to all.
I was wondering if it is possible to develop a reader to read passive tags with a range of up to 30 cm.
I don't mind using a UHF high gain external antenna or reader from Sparkfun or any other.
I just need to read passive tags from a range.

Look for "ISO18000-6C". The reader costs about $250 but you get a range of 5 to 7 meters.