Yes, I did design the board in KiCad. However, (most of) the circuit design and more importantly the code that's loaded on the Cypress micro ( system on chip ) are all taken from the 14point7 open source controller.
All i did was choose a pin compatible surface mount version of the chip, and simply did not include the LCD.
I had to buy a Cypress programmer, think it was like $30-$40 and used that to load the code.
The Cypress controller was really inexpensive, IIRC it was ~$2.00 direct from Cypress, a hand full of resistors and caps at pennies each, a 5v regulator and a mosfet for the heater. Its been long enough ago now that I don't remember the exact cost, but i remember i was hoping to keep the cost per unit under $10 (including the price of the PCB) and I think I was able to do that. I used OSHPark for the PCB, because at the time they offered 2oz copper on a 0.8mm board for basically the same price as a 1oz 1.6mm board. That being said, I could probably get the boards much cheaper now through JLBPCB or similar vendor. I went with 2oz copper because I wanted ample current capability in the heater traces, and i wanted to minimize the effect the heater current ground had on the rest of the analog circuitry.
The idea was to encapsulate the board in a ( 3Dprinted ?) connector and seal it all up, and use 4 or 5 wires to use the WBO2, +12v, ground, liner V-out and signal ground, with the option of a NB signal on the 5th wire if needed.
The board could also be used on a PCB as a daughter card as well, that's the reason for the separate sensor connector adapter board.
Edit, just pulled up my OSHpark order, it was $6.40 for 3 boards, so ~$2.14usd per board, guessing someone could get them much, much cheaper through JLB PCB or the like.