Hi Jay.
One option that you could look into is a local costume rental shop. I know of one near me (Ontario, so no good for you, but maybe you can find one near you) that rents storm trooper and Darth Vader costumes, they are not at the same level as the 501st ones, but they are pretty good and would likely not be noticeably different to an untrained eye.
Wishing your grandson strength to fight this terrible condition .