This is a good thing, the fluids are obviously helping him pretty directly, so this is a very positive sign that he's got a very good chance of pulling through this, but as you already stated, you've got to just learn to do the injections at home, as definitely the stress of the trip to the vet is counterproductive to his recovery. If you can simply give him the sub-q injection at home daily then I have no doubt he'll pull through this, as his appetite will pick up the more fluid you get in him, and the more he basks under his UVB. It's a tiny, tiny little needle, and you're not injecting much at all, it takes only seconds to inject, and it's very easy. It's not painful to them either, it's such a small needle, and doing it at home will remove most of the stress of the situation. The less you have to move him the better. You can do it!
And as Tracie already said and I'm going to reinforce, NO MEDS AT ALL RIGHT NOW! NONE! NOTHING! No antibiotics, no anti-parasitics, nothing!!!! All that will do is put him right back down the spiral he is now starting to come out of, and could likely kill him after only a single dose. Any appetite that he's gaining back will disappear. And besides all of that, any medications right now are totally unnecessary, as he has no bacterial infection at all, and the Coccidia count/load will naturally lower once his immune system is strong again. So he needs no meds at all, nor can his body handle any. And if that vet keeps insisting that his problem is a bacterial infection and he needs the Cipro, or that it's the Coccidia that is causing this, just say "I appreciate your opinion, but I'm choosing to not medicate him right now"....or you can take the meds home and not give them to him, but I wouldn't spend the money on the meds, and in addition, if you did that this vet is going to think that she was correct and the reason he recovered was because of the meds. The other side to this situation is that this vet needs to learn a lesson here so she doesn't poison any other reptiles like she did, and so she doesn't then make them worse by medicating them for infections they don't have or for parasite loads that are only elevated because of the poison she gave them. It's amazing that daily fluids and some Critical Care can correct what she did...
That's the other thing, keep pushing the Critical Care, he needs the nutrition in addition to the fluids. I know he doesn't like it, but he needs it. And usually the more you get in them, the more their natural appetite comes back...