Time will be your friend in this and let you know what's working and what isn't. Without an MRI and radiologist giving their best opinion on what a CT or MRI reads, I'd hope your vet would also been loading your dog up with antibiotics in case this is meningitis, which requires hardcore aggressive antibiotic treatment but is cureable. As for inflammations, the steroids are the way to go. Don't give up hope right now, though I know it's difficult he's going through so much, especially for such a young dog.
It doesn't present much like a tick borne disease and not a severe spinal cord injury, as that would cause sudden complete paralysis. Less severe inflammation around, disc problems, and the like (basically treatable injuries) absolutely do present the way you have described your dog's progression to paralysis. including with the bladder- it could be somewhat neurologic (meningitis or just the affect on the spinal crd, which carries info to the brain) and/or the fact he's got too much going on and not able to get up now- he could have given up worrying about proper urination habits.
Money may become an issue if the hospitalization for intense treatment continues for some time (unfortunately no way of knowing, as all dogs respond differently, but in hospital is quicker than at home with oral meds), and if an injury is found requiring surgery that too can be a big cost.
You can apply for care credit if that helps, applied for at most vet hospitals. It's a credit card for health care accepted at most vets, and when costs are high (usually over $300 to thousands) interest can be nothing to very low for the first 6mo to a year. A huge life saver for some.
Hope this helps,