You can get the detailed bill of materials on github. But basically you will need:
- 4 IN-1 Nixie tubes
- STM32F051R4T6 ARM Micro
- DHT22 temperature sensor if you want temperature display
- 30 FMMTA42 transistors that are used to drive the Nixies - so no special Nixie drivers required
- LM2937 3.3V voltage regulator
- 555 timer
- IRF730 MOSFET
- A bunch of other electronic components - resistors, caps, diodes, ...
You will also need a 9V power supply and a coin battery. And of course a way to manufacture the PCBs and a 3D printer to build the case (if you want).
Total cost of the project (with all of the materials, PCBs and everything else) should be around 120€ - with shipping included. Shipping costs are of course different from country to country but this should give you some basic ballpark figure.
Don't like how it looks with the IN-1 nixies used? You can use the PCB to drive almost any Nixie tube. So use the PCB as the driver board and wire your prefered Nixies in. You will of course need to change the 4 resistors in the middle for the correct ones based on the Nixies used. And that's really it. Everything else should stay the same.