There is another guy making what seems to be well-regarded helmets on the JRS. You can buy the kit for cheaper or fully assembled.
If you are registered: http://www.jrs501st.com/forums/viewtopic.php?f=20&t=10057
From the link:
On this topic I offer helmets made from 2 mm high gloss black high impact polystyrene.
Visor made from 1 mm aspen whit transparent foil.
Silver imperial cogs vinyl foil
Aluminium imperial discs
plastic clips
Badge
Original movie helmet size
Tie pilot helmet assembled - 230$
Tie pilot helmet kit - 165$
Helmet markings made by airbrush, color silver humbrol 11 metallic - 55$ http://www.jrsdetachment501st.org/helmet.html
Padding assembled 40$
Handmade Chestbox 181st, type B, hoses whit neoprene magnets and third hose whit mounting to belt - 185$