Best advice for non ambulatory 82 year old.

i Appreciate your time in providing input.... thanks to all!

Medical equipment has to be ordered by a Dr and there will be a co-payment, it will be an afforable amount.
If you have a transit company in your county i agree with cwillie that you should make use of their services. Other than that if you don't have the spare financial resources to obtain a van and there is no public transport try contacting eldercare services to see if the have volunteers who can provide transportation. Other than that consider trying to lease a suitable vehicle for the outings only.
Unfortunately GBS is a progressive disease so apart from making the best use of remaining capabilities there will be little improvement and likely progression.
Sorry to be the bearer of bad news but you need to have an open conversation with Dad's Dr and insist on truthful answers about Dad's prognosis then you can make the best plans going forward. Concentrate on making Dad's life as enjoyable as possible at this time but don't forget to take care of yourself. Full time caregiving is an exhausting and demoralizing so plan on regular breaks. Consider very carefully whether it is the best plan to take your Dad into your home for an extended period and the effect it will have on your marriage, family, health and the care you are ale to provide. Have you considered the possibility of incontinence for example. I do understand your commitment to Dad as your other and the probability that you made promises that you plan to keep.

It is wonderful that you are prepared to look after your loved one but consider if it may lead to resentment.

I know your question was about obtaining transport for your disabled father but I was considering the whole picture so ignore it if you wish.

cwillie is right. Used vans are available, but new ones can be upwards of $80,000 and used ones can be under $30,000, but they can have over 120,000 miles and be a dozen years old. As a woman with limited income and no mechanical skills, I hesitate to do that. We use our county's transportation system. I believe all their vans are wheelchair accessible. Their fares are low for Seniors and also reduced for those who accompany them on the rides as an assistant. The only caveats are to know when to call them to schedule for the day you need to go out, usually a few days ahead of time and our's at least only travels within our home county. We had a handicap ramp installed outside. They pull up right at the end of our driveway.

What is his prognosis in terms of recovery of his motor skills?

Talk to the SW and his pt and ot about what you will need initially and what to expect going forward.

Unless you are planning weekly outings I would rely on the disability transit services available in your area rather than investing in your own accessible vehicle.

His rehab should have a social worker on staff who will do an assessment of your home and his needs. They will then contact their medical supplier and order the equipment they feel you need. For my husband, they covered a hospital bed and a Hoyer Lift. We were not comfortable using the Hoyer, so I called med supply places until I found a different kind. It's not covered and we pay $135 a month. We also have a "Geri-chair" that we bought on Amazon. Call a meeting with the social worker at his rehab and ask what they will do and what you need to do/get. Do it now before hisntime at the rehab expires. That way you can have everything you need, Medicared covered or not, ready for when he comes home.