I've got the DIA-10 it is pretty accurate down to 1mg (might be off 1-2mg but still decent).  Its like 20 bucks on amazon.com.. Looks like they sell the DIA-20 now (up to 20g instead of 10g).

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dia-20+scale&x=0&y=0