IO, are you speaking from personal experience here?
Not personal experience. I did plan to go down to Luxor (like the OP) a while ago but gave up after the Egyptian aviation ministry gave me the run-around. Now I know that practically everybody going down there uses an agent to book the whole lot.
I know (personally, face to face) people who do go down there, and that is their story.
Sadly I also hear some appalling stories of mandatory bribery.
I would not think Luxor is a big deal. One can fly there direct from Sitia in Crete (or from Rhodos) and they do apparently have avgas, so provided one can verify the avgas it should work OK (with an overflight agent). Quite a lot of European pilots fly down to Luxor.