Why are some Cockatiels cheaper than others?

Well, the way I would start to answer this question is that the price is determined by the tameness and rarity of the bird. Say there's a Normal Grey Cockatiel that is not tame for sale, it would be selling for around £30 - £50 because it is very common and it's not tame but if it was tame it would be worth around £50 more. Then you get a very rare Cockatiel such as a Pastel-faced Cockatiel, an non-tame one would sell for around £80 as a tame one would sell for £150 -£200. You also have to consider that the tamer the bird is the greater its popularity (due to people wanting them as pets) so the more expensive it comes.

Hope this helps

HMC