These devices actually end up being kind of hard to engineer, measuring air temperature accurately especially can be kind of tricky. And then add in that for a

These devices actually end up being kind of hard to engineer, measuring air temperature accurately especially can be kind of tricky. And then add in that for a weather station it has to be resistant to the elements and low power. Speaking from experience, you end up spending more money and a lot more work going the DIY route except maybe at the high end. You can get an Acurite temp/humidity/lightning sensor that is fine outdoors and batteries last for ages for like $25. Not that there isn't value to rolling your own, just I wouldn't assume it's as cheap and easy as you might originally.