The cost of koi fish is something that people often worry about when they're thinking about taking up koi keeping. The fact is, some koi do cost a huge amount of money. However, if you buy koi when they're young, the cost is much, much lower.
Why do some koi cost so much? Well, one reason is because koi live so long. Even ordinary koi can live 20-35 years, and that means it takes a long time for them to grow to full size (about 30 inches). Roughly speaking, they may reach about 50% of their adult size after two years, 95% at ten years, and 100% at 15 years. So, full-size koi cost a lot because they've been raised for a very long time!
If budget is a concern, the best thing to do is to buy very young koi. The cost of koi fish is very reasonable while they're small. While they're just a few inches long, you can buy koi at just a few dollars per fish.
If money's not an issue and you want to fill your pond with large koi straight away, a 40 inch koi fish may cost upwards of $2,000, even it's quite an ordinary one. A rare or especially beautiful koi may cost up to four times that much.
Or you can buy koi costing anywhere between the two extremes. Aside from size, there are many factors which affect the cost of koi fish. Size and health matter, of course, but the vividness of its colour also makes a difference, plus its patterns, and the shape of its body. Experienced koi keepers have a good eye for these things, which are complicated by the fact that a koi's pattern may change as it grows up.
So buying young koi, cost-effective as it is, can be unpredictable. The upside of this, of course, is that there will be plenty of surprises in store to keep you interested as your pond develops.