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.