It's hard to imagine that once INS was developed to even just current technology, the ability to abandon hundreds, or thousands? of satellites wouldn't be all too tempting. Jamming them would be a lot more of a challenge.
Even my cheap GPS can INS for short distances.
I guess the receiver costs would be much higher, so the vendors are very pro using for free the difficult part of the project. Just think, the adjusted cost of a GPS is a 1/20 th of the cost of a Sinclair Executive Memory in 1973