Every finished sensor in this list is built around a radar module that costs a few dollars, and the HLK-LD2410B is the module the community standardized on. Wire one to an ESP32 board, flash ESPHome, and you have real 24GHz presence detection for less than the shipping cost of some branded units. ESPHome has a native LD2410 component, so there is no custom firmware to maintain.
The wiring is four connections: 5V, ground, TX and RX. If you have never soldered before, this is honestly a fine first project. The module also has Bluetooth for initial tuning through the manufacturer’s app, though once it is in ESPHome you can set every parameter from your Home Assistant dashboard, including per-distance-gate sensitivity that no consumer sensor exposes.
Buy the LD2410B specifically, since plain LD2410 and LD2410C listings differ in connector and antenna layout. Grab a few ESP32 mini boards in the same order and you can sensor an entire floor for the price of one FP1E. Just budget an evening per sensor and accept that the case is your problem.