I'm sorry to hear that Chip has not been feeling well. Since new cats have recently been introduced into your home with some sneezing, a contagious respiratory virus (such as herpesvirus or calicivirus) seem most likely. Some upper respiratory viral infections can also lead to the formation of secondary bacterial infections, which require antibiotics. An amino acid supplement, such as lysine, can help decrease viral shedding in any of the cats. Taking Chip into a steamy bathroom can also be helpful with congestion. However, since Chip sounds as though he feels so poorly, these home remedies alone are highly unlikely to be sufficient. Chip should go to the vet for an exam and will likely need antibiotics.
I understand your financial concerns, but fortunately there are some resources available to help. Care Credit (carecredit.com) can provide financing options. There are also many non-profit organizations that provide financial assistance for veterinary care (redrover.org, humanesociety.org/animals/resources/tips/trouble_affording_pet.html?credit=web_id91754962, bestfriends.org/resources/financial-aid-pets, lessonsfromaparalyzeddog.com/when-pet-owners-cant-afford-veterinary-bills/,
https://getyourpet.com).I hope that Chip is feeling better soon!