You're probably spot on, I just don't know.
The Predator is a lot cheaper in my expectation than an F/A-18 and that ought to limit some of the cost, but if you're going for a longer loiter then you are going through more of the consumables than you might do.
If it's a single run, if it's the defined target that you described with no particular defences or complexity, then it's probably a cheaper solution.