It's still 32 bit, only has 1GB RAM and it's $91 at Digikey, but the Olinuxino A20, from Olimex seems to meet just about all of your other criteria. I've only

It's still 32 bit, only has 1GB RAM and it's $91 at Digikey, but the Olinuxino A20, from Olimex seems to meet just about all of your other criteria. I've only used the A10, which is $42, but single core, no flash, no analog audio jacks, and for some maddening/expensive reason, 0.05" headers, instead of the 0.1" on the A20. It's a little behind the bleeding edge of Linux (still at 3.4), but I've been able to port an app from a beaglebone black to this with virtually no headaches. In fact, it's been nice, since there is no device tree at 3.4. Best of all, it's readily available, unlike the BBB.