Actually cost was not the driving force to implement a returnless EFI system, but rather the need to comply with ever increasingly stringent California emissions requirements in regards to evaporative emissions... caused by returning hot fuel to a fuel tank. I've no doubt that the auto manufacture's would try to use this as an opportunity to reduce manufacturing costs, but not likely at a cost to reliability or fuel economy. As any consistent failure of these components could lead to an expensive safety recall or at the very least, increased warranty work, I'd speculate that they'd not do it if they didn't think they could do it right.

Todd Bartrim

When you look at the new "returnless" fuel systems,  they are really no less
complex than the previous systems,  only a bit CHEAPER to manufacture and
install!! (corz most of the stuff is in one place in the tank - but it's a
bugger for mechanics when it comes overhaul time!!)  Cost is usually the
driving force in these things,  not necessarily efficacy,  functionality or
serviceability.