Yes, I have a rescue horse This is his before and after:
Rescuing him was very satisfying, I would do it again in a heartbeat if I ever had the money. HOWEVER, do no underestimate the costs of rescuing a horse.
Firstly, it depends where you decide to get this horse from. If from a reputable charity, you are taking a much smaller risk, and they often cover veterinary costs.
If you decide to do as I did, and buy a horse that was being sold as meat, you will, to be honest, have to shell out a fortune in vets bills for an animal that may not even be ride-able at the end. You must be prepared to either make the decision to have it euthanised, or keep it as a field companion, should this happen. A rescue horse usually winds up where it does for a reason, either it has mental or physical issues. If you want to choose this path, your best bet is to go for an unbroken youngster.
Bear in mind that you will have to keep a rescue horse in an isolation paddock (put a goat in there with it for companionship) for a month before it can be introduced to the other horses, as it will not have been vaccinated, and could be carrying minor things like lice or ringworm, or something much more serious, like strangles. Make sure you get this horse thoroughly checked out by a vet before doing anything with it.
An abused/neglected horse takes years to come right, so if you are prepared to put in the time, money and energy, it is a very rewarding thing to do.
If you are wanting a training project that has the basics established, and you would like to rehome/sell on when it is ready, you would be much better going for an ex racehorse. They have their ground work and manners established, but have had a hard start in life and really respond to individual treatment.
In the UK this year, 4000 Thoroughbreds went to slaughter. And we are just a tiny island, quarter of the size of one of your states! 80% of these horses had nothing physically or mentally wrong with them, apart from the ability to run as fast as the other racers. 10% had minor injuries, so either couldn't race to their full potential, or the owners were unwilling to invest the time and money. 9% were poorly bred unbroken youngsters that couldn't be sold due to the recession. 1% were horses so old or damaged that slaughter was the only option. 1% of horses that could not have gone on to live brilliant and useful lives.
You could get a sound, sane, stunning thoroughbred that would otherwise go to slaughter, that has been backed, or even lightly raced, for meat money. So I would say go for an ex racer! Here is mine:
Good luck, I really hope you do decide to get a rescue horse or ex racer! It is such a fun, rewarding process and you build such an amazing bond with a horse when you regain it's trust