Given the hangers on that always accompany politicians (like Remora fish) and the usual police escorts that VIP's of this level seem to need, I don't really think the total cost of a 1 hour motorcade vs the helicopter flight would be that significant, especially if you factored in police wages, fuel costs etc.
Still doesn't make it right in the public's eye and under the letter of the entitlements, but probably not nearly as bad as it is made out to be.