First thing we need is a small tea kettle to contain and heat the milk. We want a small capacity and low cost. The smallest I find is a 350 milliliter capacity - normally we're heating less than 200mL but this is close enough. These are designed like an insulated steel mug.  https://www.amazon.com/dp/B08L9PG85M

For the controller, any general purpose board will suffice. I pull an Arduino out of the parts bin.

We need a relay to turn the kettle on and off. These are easy to find - I get a pack for future projects. https://www.ebay.com/itm/292280749362

I want a small fan to cool the milk off faster after the heat cycle finishes. https://www.ebay.com/itm/381774063056

I need a small 5V power supply to run the controller. I can find one in my parts bin.

I need a waterproof thermometer to track the temperature. https://www.ebay.com/itm/182671981462

Total build cost is about $45.