[Phlarp]

A "good" GPS system (the DJI version is ~$100 by itself I think) should be able to get you down to just a few inches of precision, but yes, the market is flooded with cheap (~$20) units that aren't nearly as useful for position hold (hovering completely still) but can still give you a good lat/long and do well with navigation, distance measuring or acting as a reference sensor for a automatic direction tracking antenna. Cell phones are similarly hit or miss-- some have nicer GPS modules than others, but ultimately the user is unlikely to notice this since smartphone style road navigation only requires 10 meters or so of accuracy and a vague single position can be greatly refined in that context by knowing the road/map layout as well as the direction and speed of travel.