It's easy to see a horse in need, buy it for a few pennies, and expect to retrain it to be a good riding horse. However, who funds this? Do you and your friend have the money for board, feed, vet bills, farrier, dentist, worm treatment, emergency (and almost guarenteed) vet bills, shots, supplements, medication, etc? This horse will not be on the same feed as your other horse(s). He'll be on supplements to bring his weight up and keep him in healthy condition, and expencive feed that you might have to feed to him more than you're used to. Sometimes 5 times a day, depending on the feed.
After those expences are paid and you are hundreds or thousands in the negative, you have to worry about training. What do you know about this horse? Is she broke? Halter broke? Has she even been backed? Do you have the experience necessary to train a rescue? The resources? The time?
After all this, what's to say the horse will sell for more than you spent on him? If he doesn't, are you, as your family, willing and capable of taking the loss as your own, and knowing he's going to a good home?
There's a lot to think about. I would try giving A/C a call first.