Ok then.
I downloaded a map of my country a few years ago - not any DJI map though, just a standard WMS protocol tiles which can be then used for `mapserver` or merged together and opened with `QGIS`. I used a few scripts I found on Github. The source of the maps was Geoportal, and resolution was 25 cm/px. It took considerably more than 500GB actually, but you can reduce that if you download lower resolution - many services don't even provide 25 cm/px, but only 1 m/px.
You just need to figure out which service you want to download from, and then prepare a script which does that. I finally switched to using `gdal_translate` to download only the areas I'm interested in rather than the whole map. And the command `gdal_translate` don't tend to change often, so my scripts from a few years ago would probably create a a good map today (this way I can get an updated map every few years). This gives a TIFF file which can be opened in QGIS without any additional processing (if you use `-of GTiff`). You just need to find (or write) an XML file which described the service you're downloading from.
And if you mean downloading for the Dji Go app - that would require writing a simple app which uses the same map API and creates the large cache, then copying that cache to Dji Go - a bit more work, but nothing an IT student can't handle.
EDIT:
Also worth noting that every map service has a specific license. You're typically not allowed for commercial use of the data you've downloaded for free.