Horses as a whole have a wide range in prices that can depend on age, breeding, showmanship and capabilities. You do not mention how old your daughter is. If she is young a Shetland pony or Welsh pony might be a good breed for her as they tend to be smaller. Teens on up could go for any breed that would be suitable to their riding ability and what they would like out of a horse. If you do not know too much about horses it might be good to have a good trainer help you choose a horse for your daughter. They are well-versed in matching horses and ponies and riding abilities. Perhaps your daughter is taking lessons to learn to ride at the moment and that stable has a qualified trainer that will help. They will require a fee for their service but it can be worth it to make sure there is a proper fit between horse and rider. As for price, a good trail horse or pony should cost less than $5,000. That is just a top amount as you might find one much cheaper depending on your area of the country and the market prices. I had spent $1,500 for my welsh pony/thoroughbred that was good for trail riding as well as low level horse shows back in the 1990s. If your daughter shows and wants a top quality show mount for hunters, jumpers, dressage or any of the western riding disciplines then expect to pay more. Much more in some cases. The stable I used to ride and show out of had show horses worth $150,000. Of course, horses come in many in-between prices too. As I said it might be best to talk to a trainer first to get an idea.

Sources: http://www.equine.com/horse-prices.aspx