As kezo rightly points out, the actual cost is over £19k (3 yr) or £26.5k (5 yr) and it will in fact be more than that with future benefit increases taken into account. I don’t think I’d outlay that for a mid size base model Audi. That sort of outlay would be a major contribution towards the private purchase of a better car, which I would then own.
As others have pointed out, most Motability customers do very low mileages. I wonder how many people really do the maths when it comes to their choices? Many would surely be far better off financially if they used taxis!