Most of the major vendors are already assembling x86 laptops for the far larger Windows market, it's cheaper to just reuse those models for ChromeOS instead of designing a special ARM design, which in turn due to lack of scale are priced similarly to their x86 counterpart. Price sensitive customers thus don't see that much saving.
Battery life is nice, but I doubt there's that much market yearning for a cheap laptop with long battery life. People who really need large screen for long work without wall power either go at x64 (which can reach 12 hours on mid range now), or change their workflow to use Android tablet. The ubiquity of USB charging port that can power the laptop (or at least top it up while standing by on lunch) also means even if an x86 laptop may not last an entire day, the owner don't have to suffer the inconvenience of carrying around the power brick.
There won't be that much saving due to the lack of scale. The mentality of (normal, well adjusted) people around me is to dismiss laptop entirely as a personal computing device, they have their phones and tablets that are far easier to use. For them to get a laptop would imply they're forced to, because there are Windows apps unavailable for Android/iOS. A cheap Arm notebook is useless for them (unless Microsoft somehow decide to work with Mediatek and the rest for cheap WoA devices). Chromebook never gained popularity in my country with lack of reliable and affordable internet access so the realistic OS would be either one of those Linux distro that support ARM (but in turn, most people don't care about Linux), or Android, in which case it's still far more natural to just get a tablet with a keyboard attachment because Android desktop experience and the apps ecosystem aren't there yet.