UCAVs may be cheaper to purchase as a unit. But they are not intended to fly for the 6,000 hrs life of a FJ aircraft.
Hence, you have a training problem. If some form of ground control is to be utilised, people must train regularly and in so doing, you rapidly use up the system life of the UCAV and need to buy some more. Please do not shout about simulators, you have to use the real thing to determine its actual limitations amd weed out the 'bugs'. It is lethal to base operational plans on a defence contractor's optimistic claims for the capability of its product only to find out the hard way that the thing does not work as advertised. Consider what the 'cost' of that situation could be.
Even if the thing is simple and can sit on a shelf until required, you still need to carry out some maintenance activity, which equals cost.
Finally, we never, never, never fight the battle we plan for!!! So the in-built flexibility of having the human, right there in the air platform 'close' to the difficult bit, is vital when it's 'all change'.
I am not a luddite, these things have their place and will, no doubt, develop. But using simple unit cost as a prime justifier for following the UCAV route is a flawed argument. Even the Americans have realised that one.
lm