My holistic vet recommended a human probiotic by Jarrow to give Pookie after his dental surgery, since he was on antibiotics. She wasn't a fan of the one I usually give him, but I have him back on it because the Jarrow capsules were small and several times I would shatter them trying to pry them open. I was afraid some of the shattered capsule would get in his food. But in a pinch, a human probiotic will do. The one I give him now is this one, but that's because my pet food store carries it:
http://www.wholisticpetstore.com/index.cfm?fuseaction=product.display&Product_ID=553&ParentCat=50.
I checked my books and the only suggestion I found that might be useful is to add water to kitty's (wet) food to make sure he/she doesn't become dehydrated. I did read that Aconitum 30C is the homeopathic for colds. It may also help with fever.
If it's a high fever, definitely call your vet. If it's a low-grade fever, the kitty may just need time to fight it, though I personally still think the probiotic would help. I'm not comfortable giving human dairy products to cats, but that's just me. It may be perfectly fine, I really don't know. I'd be interested in what the other folks here recommend.
Colloidal silver is anti-bacterial, anti-viral and anti-fungal. My holistic vet doesn't think you can give it to cats, but I have given it to Pookie short-term (after his dental) and he seemed fine with it. I only added a couple of drops to his food each day. Whether it helped or not, I couldn't say. You can find it at most health food stores.
One other thing: if this is the kitty that got vaccinated while sick, it's possible that the fever is a reaction to the vaccine. Depending on what the vaccine was for, there are homeopathic remedies that can be used to help. Thuja is used for everything EXCEPT rabies. The homeopathic for rabies is Lyssin. (And you may want to have the vet report it, though they probably won't. I think there's a way for you to report it as well, but I'm not sure).
I know finances are stretched right now, so please don't feel like you have to use all of these things. I just wanted to put as much information out there as possible. I would definitely add a probiotic, and add the water to the food. Neither will hurt, and they may help.
I hope this helps (at least a little)! Sending purrs that everyone feels better!