HA! found one. http://www.engtaobao.com/item/559452178207.html
STM32F070F6. i think this might have been the one you were referring to, westfw, and i got it confused with the 072. this guy on taobao, very sensible: each one is USD $0.16... he then charges USD $28 for shipping (flat-rate). so... buy 1,000 and you're good. buy 10,000 and you're laughing.
what that means is though that i'd stand a good chance of getting it reaaally cheap in the huaqiang road markets.
even the prices on ST's web site - $0.50 or so for 1k volumes - are good. crystal-less USB operation, UART, GPIO, SPI. i could put up with that. hell i'd be happy to try to run the SPI wires over to it and wire up SPI and a CS to that last remaining GPIO on the 471, try making it a slave SPI device to get better data-rates when communicating on its USB interface. up to 18 mbits/sec full duplex where the USB interface actually only goes up to 12.
the only thing: it's not OTG, it's plain USB. but still, plain USB is better than a kick in the teeth.
ha, connecting it to the SPI interface would allow direct boot-level reprogramming of the 471. HA!
still owe you a reply on your last message, westfw - haven't forgotten about it.