They still have effectively no RAM, though. I clicked through for the first one I saw with as much as 256kB of RAM, and it was US$35, the same price as my 1.5GHz quad-core ODroid C1, which has 1GB of RAM. I don't understand this. Is it purely a power efficiency thing?

The NUCLEO-F411RE has a product page but doesn't seem to be for sale on that site. Where can you get it?