Let's measure power output from Eachine TX805 that is supposed to be up to 800mW. Well, it is not. It matches the specification only at 200mW and 800mW is just not there. But, well, it's only $16 and when used at 200mW or 500mW it works quite well.

RF power meter can be purchased for really cheap. Surprisingly, it is a pretty decent hardware too...