I've found the safe-guard (10% suspension) liquid to be the most cost effective and the easiest to dose accurately.
It comes in three sizes, the larger you buy, the cheaper it is per unit:
125ml
http://www.jefferslivestock.com/ssc/product.asp?CID=2&pf_id=00290131000ml and 1 gallon
http://www.jefferslivestock.com/ssc/product.asp?CID=2&pf_id=16380