[sberder]

I don't know of any cheap outdoor sensors, they are more tricky than indoor as wind (air flow in the sensor), temperature, humidity and dust become more of a prominent problem. For a cheap sensor, laser egg publishes API endpoints to get latest data. You can also fairly easily add a plantower to an arduino/raspi kind of setup. Pantower is a sensor that will give you reliable output OOTB, can be improved but good enough.