Hi G,
In short, then no, Egypt isn't expensive. At least not for a Dane like me.
You will find that El Gouna is more expensive than Luxor, specially concerning drinks.
Another thing that can put a large dent in your pocket is entrance fees to sites, but seeing that you are going on a cruise, I guess you have already bought a sightseeing package?
Eating and drinking in Luxor is fair priced, but again, drinks can be expensive.
I don't know how many tours you have or if you plan any tours, so if you could tell a little about your schedule, then it would be easier to come up with an amount to bring :-)
Louise