I think rescuing is a great alternative to buying. Sure there is normally a price tag with them-either to help cover some of the medical expenses that a rescue group has put into them, or to buy them flat out at an auction...but it is extremely rewarding. An auction you are kind of putting yourself out there to "get what you get", so it is taking a big risk...and if you're not in the financial position to fully recoup one of those, I would look moreso into a group/organization-than a sale/auction.
I've had 2 experiences with rescues.
The worst case was a mare I was supposed to be looking at to BUY, and when I showed up, she looked like she hadn't eaten in 6 months, her overgrown, beat up hooves had two, diagonal shoes on-that were growing into her feet...she was scared of her own shadow, hitched in her hocks, but I felt just TERRIBLE. I offered them $1000 for her, and took her home with me. She actually wound up having an old leg injury, and was psychologically/emotionally SHOT and was literally dangerous to ride (she reared up and fell backwards right on her rump about 3x after just putting a saddle on, and liked to haul booty BACKWARDS once you got on her). They told me that she did jumping, barrel racing, dressage, western pleasure, cattle roping, halter and trail riding...and was just fine for any sort of rider. To me, the fact that she would not ever be used as a riding horse again was fine with me...I was just thankful to have helped her out. It took a year of reconstructive shoeing to her feet, LOTS of TLC to get her to come around (although she remained VERY skittish/head shy/etc.), lots of good feeding, and time time time...but she made a beautiful pasture ornament, and I gave her to a home where she was going to spend the rest of her days grazing happily, and possibly making some beautiful babies in the future.
The other was a filly I got off the track, and out of a sale barn. She needed some stall rest, but after her rehab period, the vet pronounced her sound for just about anything my heart desired.
After I found out that I was pregnant and wasn't going to be able to work with her for some time (and it just wasn't fair to her!), I found a wonderful family about 2 hours from me to give her a home on a "No Sale" contract (I love the mare!).
It is VERY possible to find a nice, sound horse who is dying for a home of love and TLC...if it's truly what you want to do-GO FOR IT. Do some research and read up on a few things. It is absolutely a great feeling when you can transform a horse into something they WANTED to be, into something they BECOME.
Good luck!!