While I think its great your friend is willing to get back on the wagon there are far fewer guide horses in the country than guide dogs. The cost is of course also larger as they do need a barn outdoors, even if it could be smaller than for a regular sized horse or even a pony.
Guide horses have the same rights as guide dogs and can accompany you into stores, etc.
You can find more information about guidehorses here:
www.guidehorse.com