I am just going to attach the pictures in order, but here are the steps.
1 Hobby Knife
1 Pin Vice w/ 1/16", 5/64", and 3/32" bits.
1 Piece of pinning material - very short(I used 3rd ed Rhino roll bars)
1 Arm with clasped hand(SM grenade hands work very well for this)
1 Chalice Base(this can be anything you want. I used the top of the old 3rd Ed SM backpack banner pole)
Carefully cut the handle side of the MeltaBomb off right above the ring. This will form the lip of the cup. File/Shave until it is fairly level.
You can trim the blocks off the side if you like. I didn't bother. I like them there.
Trim your base piece.
Starting with the 1/16" bit, begin hollowing out the top/flat side of the cup as close to middle as possible. Be careful not to go down too far.
Flip the cup over to the uncut rounded side. Put a shallow pinning hole as close to center as possible. This will be difficult with the curve as well as there will probably be a lip from where the mold wasn't aligned completely.
Switch to the 5/64" bit and hollow the cup out a little more. Switch to the 3/32" bit and repeat.
It is important to gradually increase your bit size when hollowing this out because if you use your largest bit first it will be very difficult to hollow as well as you run the risk of splitting the plastic. Start small and work your way up.
Use your pinning material and glue it into the pin hole on the bottom of the cup.
While that sets, use your vice and pin a hole through the arm of choice. Try to be as close to center as possible.
Assemble the Chalice by placing the pinned side of the cup into the pin hole in the hand. I put a drop of glue ontop of the hand hole so it coats the pin as it's inserted to hold it in place better.
Attach the bottom pice you chose to the bottom of the hand. Pinned, preferrably, as close to center so that the chalice and bottom piece line up as much as possible.
And there you have it. 5 minutes of work to give you an effective and simple chalice for your Sanguinary Priests! Hope this helps people in their endeavour to model their priests so they don't have to say "Oh. He has a cup too...somewhere." and it will please all the WYSIWYG players in your game groups. Just don't forget the Bolt Pistol holsters on the leg!