Well, you will have to pay more than with existing ceilings, because the air volume to be heated is larger and the area of the exterior walls in relation to the heat-emitting surface increases.
But since the insulation etc. will keep the heat inside and as already mentioned the heat-emitting surface is the floor, the whole thing will not become excessively uneconomical.
Additionally, you have planned a controlled residential ventilation system, and this will distribute the heat throughout the whole house (albeit only slightly). With or without an intermediate ceiling, you will have relatively homogeneous temperatures on the ground floor and upper floor, among other things, due to the controlled residential ventilation.
No matter how you look at it, heating costs will only differ marginally. Provided the roof surface is sufficiently insulated.