I am sorry to hear you are worried about Smokey. My name is Rebecca. I am a veterinarian and will do my best to help.
Is he paralyzed in all four legs? Are his legs stiff, or limp?
Botulism causes a flaccid paralysis, where the limbs are limp but cannot move. It usually starts in the hind legs, then moves up to the front legs, and then gradually moves into the the muscles that we use to breathe, resulting in suffocation. I searched on a vets only website; there has not been a case of botulism seen in cats. Cats and dogs are resistant to it; people and horses are sensitive. There are tests that can be done to confirm botulism your vet can do; I would do that before just randomly giving anti toxin without knowing for sure what you are treating. Tetanus is also very rare in cats but can cause paralysis, and requires a different anti toxin, so you should know what you are treating before buying expensive anti toxin.
I suspect this paralysis is due to something else seen more often in cats, such as low blood potassium, low blood sugar, or a problem with his nervous system such as stroke, a tumor in his spinal cord. Tick paralysis can cause the same kind of paralysis as botulism, and is treated by either finding and removing the tick, or applying Frontline to kill ticks.
If your vet can't tell you why he is paralyzed, I would consider consulting a neurologist for a second opinion. That is what I would do for my own cat.
Let me know what else I can help with or answer. Rebecca