What is the best way to buy a pony?

Type Petlink into google and click the horses tab.

Another worthy resource, is Horse Deals. It is an Aussie mag that can be bought from most newsagents. Horse Sales are great as well. Prestige horse sales are best though.

Horses are usually for sale between $1000 - $4000 depending on the quality of the horse. I've seen a great horse go for $65000 and my neighbour bought one for $1.