GPS app to aid in geotagging Photos from my Nikon D3300 DSLR camera

Hi,
Brand new to the forum and I need help.
I'm an amateur photographer and I want to start selling my photo's. The problem is that a lot of sites that buy photos want a geotagging embedded in the photo but my Nikon D3300 doesn't have a gps in the camera and a gps attachment is $200.
I...

GPS app to aid in geotagging Photos from my Nikon D3300 DSLR camera

GPS app to aid in geotagging Photos from my Nikon D3300 DSLR camera