You do not need to spend $40 per sensor to build a solid smart home. I have been running cheap Zigbee sensors from Aqara and Sonoff for years and most of them have been rock solid.
Aqara Door/Window Sensor ($9)
Tiny, reliable, battery lasts about 2 years. I have 12 of these on every exterior door and window. Response time is under 100ms through Zigbee2MQTT. The new P2 version supports Matter over Thread too, but the classic Zigbee version is cheaper and proven.
Sonoff SNZB-02D Temperature/Humidity ($10)
Has an LCD display so you can read the temperature without pulling out your phone. Reports to Home Assistant every 5 minutes. Battery lasts about 18 months. I have one in every room for climate automation.
Aqara Motion Sensor P1 ($15)
Adjustable detection sensitivity and timeout. 5-second re-trigger time (most cheap sensors have 60-second cooldowns, which is useless for lighting automation). Mounts with the included adhesive or a standard screw.
Sonoff SNZB-06P Presence Sensor ($13)
Uses mmWave radar instead of PIR, so it detects presence even when you are sitting still. Game changer for rooms where you work at a desk. Needs USB power (not battery), but it is cheap and effective for its price point.