Those are still much more expensive than the lowest-end. I think they cost around $100 last I heard, and a currency conversion on the amazon link there gives $104, which seems to confirm they haven't gotten cheaper.
If you sort this site by price http://www.snapdeal.com/products/mobiles-mobile-phones/filte... you find the cheapest smartphones are about 1500rs. That's about $25 (according to Google). Most of them run Android. Though, once Windows Phone 10 comes out, I'd be interested to see if that's a better UX at the ultra-cheap end of the spectrum. Nevertheless, Android is currently the OS of choice at the low end, wherever you draw the line on acceptable UX. And the latest and greatest Android is available for about 4800rs, or about $77, running on a quad-core SoC.
As for how that's done, it's because Android can aggressively "swap" (really serialize and reconstitute)background components out of memory, and it can do the same to whole processes. You can actually watch your Android app instance switch PIDs, as it comes back from having had all the components, and the underlying runtime instance, killed. Now, there are some fat slovenly apps out there that might not be happy with life in a very limited machine, but I bet those 1500rs phones push the minimum specs pretty damn hard.
