I checked for neck size dies, and Midway sells them for $24. It's a collet die. Here's the description from the website:
This die sizes only the neck to preserve the perfect fit of fire forming. A collet squeezes the case neck against a precision mandrel for a perfect bullet fit with minimum run-out. No case lube is needed. Cases last about 10 times longer. Only reload cases that have been fired in you firearm. Not recommended for autoloaders, slide or lever action guns.
Notes: Collet neck sizer uses a collet to squeeze the case neck against a mandrel, creating a precisely aligned case neck while reducing runout.
They list .30-06 as out of stock with backorder OK. I'm tempted to get one for the .303 British, to try to get longer case life.
BTW, I do the neck size thing with .45 Colt, because full length makes the cases rattle in the chambers and is completely unnecessary for the kind of shooting I do.