"1. Is there a material cost benefit to the more expensive dies?"
Not much, certainly not for any of the common brands and conventional designs. SAAMI dimensions are a tolerance, anything inside that range is fully "in tolerance", and they all normally accomplish that, so there is as much effective difference between individual dies of the same brand as there is between brands.
Forster BR and Redding Comp seater dies for rifles are "better", on average, than conventional seaters but not by a lot and a good conventional seater will do as well. But, none of the other so called "comp" dies are in the same catagory, they're no better on average than the others. The expensive micrometer seater heads don't add a thing to the product, they are only user features that can easily be used or not.
Lee's collet neck dies are probably the better neck dies on the market for factory rifles but they have a moving part, it's not a simple 'push the case in, pull the case out' thing, so some people have trouble using it correctly. The Lee collet neck die, correctly used, and used with a body die is probably the ideal combo for good sizing and obtaining straight necks without accuracy damaging excessive "bullet tension." (The ideal neck inside diameter is ONE thou smaller than the bullets, no more.)
I've used all dies except Dillon and while there are some trivial user feature differences between brands, the 'best' is purely a matter of taste - and chance of the tolerances. Some like this or that feature but others hate it; love/hate doesn't change the quality of ammo that can be made with any of them. And neither price nor external finish matters to the end product.
"2. Is there a material cost benefit to the more expensive turret presses?"
None, stick with your single stage. Presses don't exactly make accuracy but the more rigid a press is the easier it is to do consistant work. No turret can be 'rigid', the head couldn't turn if it was. Lee's turret is probably the best of its type because of the way they attach and support the head that limits the turret's up-ward springing under pressure better than any center mounted head can be.
There is precious little accuracy advantage to costly or massively strong single stages either. Great press strength helps when massively reforming cases, not so much with normal reloading chores.