Spadge,
The Candy finishes are £70 + the cost of the machining or you can polish yourself. I'm not sure about the black without checking, as the powder "may" be cheaper, but at least you know a worse case scenario....

The high cost is due to the amount of time it takes to mask all the bits off that you don't want the powder coating to adhere to. If you wanted it all one colour, it would be considerably cheaper.