cat has cracked paw-pads & scabs on ears

[regularguy]

My 5yo maine coon female has suddenly developed a condition that two vets at animal hospitals cannot diagnose. They both did blood tests and found very elevated white counts but nothing else. They gave anti-biotics (orthox 22.7mg).
The cat (Comet) suddenly started to show signs of dry, cracked pads on her paws which also became inflamed. Her ears started to get very dry and crusty on the extremeties. The condition has spread also to her lower jaw. She is loosing the fur in these areas also, but I don't know if it is part of her over grooming the areas. She has to be brought to the food and water and then she hobbles off and hides. even though she is eating almost as much as she normally does, she is loosing weight. Two of her paw-pads have now become infected around the nail and we have been smearing bag-balm then wrapping with gauze to keep moist. There is some improvement in the condition of her ears, but the condition has spread to the other parts of her body as mentioned. We pull scabs (loose from the bag balm) and apply the ointment three times per day.
The vets now wants to do a biopsy for $350 which we cannot afford. This has already cost $300 times two visits, and they are stumped as to a cause.
It seems that this skin condition may be a symptom of an immune difficiency from another disorder(my own guess from reading many forums) but what could it be. Please help. It has been almost three weeks now and I am worried for this cats health.
Thanks
Pete