I wanted to use STM32F405RG for this, so I needed to update the design with lessons learned from my breakout board. I also replaced ESP-03 with ESP-12E/F and replaced all 0805 packages with 0603 as well as adding an extra status led. I still lack support for ESP-01. As a result of the smaller 0603 packages I got more space and this is single sided assembly only. I have soldered quite a few boards with 0603 components and yes they are small, but I never get them wrong anymore.
I have not done cost calculation yet, but I estimate ca 20-25.- USD in component/PCB Cost.
Notice the silc drawing in red on the MCU and W5500. I recommend that you always remove that silc on tight chips because it makes it difficult to inspect pins after soldering. The white line is difficult to distinguish from solder waste. Also avoid ground plane on mount side if your assembling yourself. This is why I wanted single sided assembly so I could use ground planes on the other side. The adapter is quite small 80*50mm.
I did consider replacing the tiny Murata x-tal used on the MCU, but looking at the size of the alternatives realizing that my x-tal cost 21 cent compared to 5 cent on the larger I ditched the idea. I have soldered quite a few Murata x-tals now and I never get them wrong (expect for the ones I drop on the floor). Those HC49C pack with 2 x caps each look gigantic in comparison. I will upload New schematics once I am done.