Drone + GPS unit? (GCPs)

[FrostBite]

 I wanted to get some kind of GPS unit for getting better data through Ground Control Points.

I was wondering what you all would recommend for a cost - effective setup.

Is there some kind of antennae I can sync to my phone with an app? Like SW Maps?
Or would I have to buy a whole antennae + GPS unit setup?

What do you all recommend?

Thanks!