Check our Cranbury Sale Stable. It’s an auction house, so the horses are on the cheaper side. That being said, it isn’t gauranteed that they will have warm bloods or thoroughbreds. The horses that they do have are typically underweight and will need some TLC. There’s a bunch of OTTB’s for sale all the time that are fresh off the track for very cheap.
There isn't really a place per say, only websites you can go on. Thoroughbreds off the track are pretty cheap, usually around couple thousand and if they are really well trained the highest I've seen are around 30k. Warmblood's are obviously more expensive, starting at around 20k. There are cheaper ones, but they either have a problem/ are pretty old or are young foals that aren't even a year yet. So I would stay away from those if you are planning to buy a warmblood. More quality ones would be 60k-80k and above, and the Grand Prix warmbloods are in the millions.