off line gps navigation app?

I use OSMand + It uses downloadable maps and has available topo lines as an extra .
It seems to work well .

You've come to the right place, everything you need to know is here, https://www.exploroz.com/traveller
...don't know what your idea of cheap is though and the full suite of offline maps is close to 4GB from memory but it's in west, east and central if space is a problem.
I've just put in on a lenovo Tablet and it's doing the job. I also have it on a Win 10 laptop where I enjoy the large screen even better.

I have spent the last couple of months looking into the same thing for an upcoming trip to USA and Route 66.

My conclusion is that Locus Maps tick all the boxes for what I need plus it has many feature that can be used to adapt it to you liking.

In particular I want lane assist, speed zone warning, import file types like kml/kmz/gpx, off line etc and Locus has them all plus many more.

You can get a free version or pay $10.99 for the Pro version which has no adds plus unlimited map downloads.

I intend to plot my daily drives before leaving, working on my desktop using Google My Maps or similar.

If all you want to do is get from point A to point B using the fastest route, you can used Google Maps. What I want is to plot a scenic route but Google will not follow your way points but Locus does.

OSMand + is another that is on my list but Locus is more flexible.

Only negative I have with Locus is the lack of a pdf user manual but most of them are the same. Locus has a very good online wiki style user guide that covers it all.

You can download maps of different areas from Google maps and use them offline. I did this when I went to hawaii. its free

Cheers
Tom

Hello

For street navigation I use Maps.Me (for android) when traveling overseas - download relevant maps before you go so no data roaming required. Probably no good for "outback" navigation but you do not specify your requirements so maybe what you are looking for.

Cheers
Greg

I use Copilot GPS when OS. When you buy the North American maps you have a licence for all of it, but if memory capacity is an issue you can choose to install only the parts you need.

It has lane assist and it is easy to plan your trip ahead of time, and save it. Best on a tablet for that, but you can do it on a phone. The licence allows you to use it and the maps on multiple devices, so you can plan on a tablet and use a phone for a display when driving.

Its coverage of minor roads and tracks in North America is excellent.

Early versions had a Windows (and probably Apple) desktop program which is excellent for planning but sadly I think that's gone now. I still plan on it then transfer the trip to the mobile devices that have the up-to-date app and maps and then tweak it if necessary.

It's Aussie maps are also excellent with better than average coverage of minor roads and tracks.

Cheers