I would buy 4GB SD or MMCplus card and card USB reader. It can be found for similar price and you can remove the card and use it in the tablet or use it as usb stick inside the reader.

I have recently bought Transcend 4GB MMCplus card and this http://www.sharkoon.com/enghtml/usb.htm#xcplus reader. Total price was 834+239=1073 CZK ~= 38€

Read speed in the reader is ~ 14MB/s, write is ~ 3.5MB/s