Arduino101 is not an ARM. I'd say that both 101 and MKR are in a similar price range to Uno. Under $40, anyway (and they both include BTLE communications.)
Yeah, you would think that with smaller ARM chips selling for about the same price as an ATmega328, you might see an ARM board like Uno at the same price as Uno. I guess that would be nice - I'm not sure that anyone would buy one, given the large number of "other" manufacturers selling more powerful ARM-based boards at lower prices (TI Launchpad, ST Nucleo, Freescale/NXP Freedom, Cypress Pioneer, Teensy, Micro:bit, Silicon Labs...)