The value placed on a horse is not random. I will give you a breakdown on how prices are established.
1. Stud fee. (average $1500-$3000.... it can go higher) Semen has to be shipped or breeding may take place at barns with skilled handlers.
2. Mare care (through pregnancy). Ultrasounds and routine check-ups to make sure the mare carries full term. (average varies so we'll say $1000)
3. For this reason, when the foal hits the ground his starting value is double the price of the stud fee (as a general rule). That is because you will have invested this much into him already. Bare in mind---- the basic upkeep (feed, hoofcare, etc.) is not even considered into the equation.
4. It is ideal for breeders to sell horses young so that they have less money tied up in the horse. A double edged sword for the buyer because if they buy young, they get a deal but they also have a horse they have to maintain for years prior to reaping any "benefits".
5. At 2-3 years of age the horse's value increases if it has now advanced into training. This is where bloodlines come into play because good breeding should produce horses with great trainability and performance. (On average it costs $1000 a month to send a horse to a reputable trainer. You might be able to find some that are cheaper... say $600 a month.) On average it takes three months to green-break a horse. Ideally, the more training a horse has the more his value should increase. Unfortunately, this is not always the case unless the horse is well bred and even then it varies.
6. Horses are valued about like cars. A reliable used car will cost you about $4000 bucks. It does the job pretty good. A car cheaper than that is going to have issues and will probably start nickel and diming you. A $25,000 car has a lot more amenities. In the instance of a horse, this means the horse is a luxurious partner with push button sensitivity or he is high performance.
I hope this helps. There is a video of a horse who's owner turned down a $300, 000 offer. I agree with the owner's decision and actually consider $300, 000 almost insulting. The horse proves his worth as a stallion, a partner and an athlete. To see an example of this incredible specimen, google "Orpheo Merlin" and draw your own conclusion.