I wouldn't bother with powder coating, get them painted at a decent bodyshop - you'll end up with an arguably better finish, and a coating that is more durable (I've not had powdercoated wheels myself, but from what I've read when I first looked at doing my VXR wheels black, they chip rather than pit and it makes further refurbishing a PITA).
You could probably have them painted for £200, and a set of mint Anthracite wheels should sell easily on the owners club if you don't like them - I got over £100 for one single standard wheel.