I have an Ambient Weather WS-2902C feeding to CWOP out of the box. It also lets you configure custom endpoints (REST based), so I have the data feeding into my own system and logging into a db that I can use however I want.
Inside its esp8266 based. Currently sells for less than $200.
I also have a WS-2902, and years ago I tried to publish to CWOP. It was not easy without installing a number of Python dependencies and running your own process to constantly poll the weather station and then publish to CWOP. If I remember correctly, Ambient would publish direct to Weather Underground at the click of a button. Alas, WU has sort of deteriorated over the years. My information here is 4-5 years old.
You have to use their WeatherBridge app to configure it. They have some info for CWOP on their FAQ site [1]. I believe that same app is where you set up your custom endpoints (it's been a few years since I did it).
Inside its esp8266 based. Currently sells for less than $200.