agreed , I wouldn't spend $2,500 for an MRI . This is a 10 year old dog, with a non-cure condition . So I would do everything in my might though to mitigate the situation , slow the decline as much as possible and give ex life extension with as much quality as possible.
give "good" source of protein , antioxidant , anti inflammatory , sources of choline , B12 , Foods That Improve Myelination | LIVESTRONG.COM
bone broth, anything to help build collagen , selenium/magnesium .
Wobbler's which is associated with Doberman and Great Danes and GSD , is something which a friend of mine is experiencing with her young Dane . This is something I found for her New hope for treating wobblers syndrome
have no idea if it works but this video clip is very interesting.
essential fatty acids -- high omega 3 - helps with brain and nerve development and an oil (fish) that has a good dose of DHA which will help with myelination for nerve impulse MAY BE one of the ways to affect a preventive course against DM .