I know this is an older post,but....I have cleaned up quite a few pieces of cast iron cookware so I will share my experiences with you folks.
Never and I mean NEVER sandblast a piece of cast iron cookware!! It takes FOREVER to get the sand out of the pores!
Easiest way I have found,is to fire up your bbq grill and run ALL the burners on HIGH. Stick the piece that you want to clean, in the grill and walk away for a couple of hours. Just let it cook. Shut down the grill and let it cool down all by itself and KEEP THE LID CLOSED while it is cooling off! After it is cool,take a couple of paper towels and just wipe the rust off. It will come off in a fine powdery dust. Now,fire up that grill and set it on high AGAIN. Coat the cast iron all over using cooking oil or lard. Cover every square inch of the piece with oil. Put it back into the bbq grill and let it cook again for an hour or so. Let it cool down the same as last time. VOILA' you have just rescued a another fine piece of cookware!!