ETA: Kay, thanks for the updated post with how you have been managing his care thus far. It sounds like if this is managed well, he has a chance to make a full recovery without surgery. I am not sure why the meds were discontinued, when he is still exhibiting problems, they might need to be resumed, but only a vet that has examined your dog can make that call. Therapy or other holistic treatments might also help during this period. And again, a vet that specializes in sports injuries might have an innovative approach that will have greater results than traditional rest & medicine.
To everyone else reading her post, just because Kay listed the costs of different treatment options, doesn't mean they are avoiding surgery based on cost. It is expensive, so if it wouldn't be successful, there's no point in going forward with the expense, & recovery. This is where a 2nd surgical opinion is important, and also therapeutic treatment beforehand - to lessen the need for surgery, & increase the chances of a positive outcome.
Original response:
I don't really get a good feeling about your vet from what you have written. I'm not sure if it just isn't translating well, or if your vet is not as proactive as she should be.
Medication only, with small improvement, & now your dog is on no medication with a hope for continued improvement is what I am taking from your post. And if there is not continued improvement, they are recommending either a surgery or adaptive device.
First of all, are you making sure to eliminate activities that could make the slipped disc worse, such as not allowing him to jump up or off furniture, etc.? What I know anecdotally, & what I was able to find online in a brief search, your dog should have been confined, preferably in a crate, for a number of weeks while on medication, and then gradually allowed freedom of movement as he improved. http://www.petmd.com/dog/conditions/neurological/c_dg_int...
In addition to medication, I know a number of people who engage in therapy for their dogs, either cold laser, ultrasound, chiropractic or water therapy (swimming). These have a number of different benefits, & some may be appropriate for your dog to help him continue to heal.
Considering your dog is only 4 1/2 years, if he is a good candidate for a successful surgery, that would be an ideal option. If surgery does not come with a high risk of success for him, an adaptive device like a doggie wheelchair is an excellent option. I know many people who have dogs that have utilized them, either for recovery from injuries, loss of limbs (cancer/injuries) or degenerative diseases that caused rear paralysis. The dogs still maintain a quality of life, as long as you are able to adjust your lifestyle & home environment to let them continue to engage.
I highly recommend you get a second opinion from another vet (& possibly a third from a holistic vet, such as a chiropractor). If you have the option to get a consult with a sports medicine surgical vet, that would be ideal (check with local kennel clubs in your area, or training facilities that specialize in competitive activities, such as Flyball or Agility for referrals).
I'd like to give your vet the benefit of the doubt that she has the best interests of the dog in mind, but her bedside manner, & lack of proactive treatment in this case is very underwhelming, & if this were my dog, I would want more information to make sure the right steps were taken to help him get better.
Good luck! T. :)