Hello,
I had my rims sandblasted and powdercoated about 6months ago got them done for $60 each, prices will vary depending on the finish you want, mines a metallic pearl therefore the price is slightly more.
I got it done at:
Mr Clean - Blast & Coat - Padstow
Unit 3 / 89 Gow St Padstow NSW 2211
ph: (02) 9790 4758 Powder Coating Services
Takes 1 working week possibly less, you need to get your tyres removed on your own so thats another $30 or so and have them refitted when you are done - which is another $50 inclu. valve caps and balancing. Thats probably the most irritating bit as you'll need to borrow a set of wheels or a week or so.
In the end it's worth it, here's the end result of my adventure:
Colour is "Black Onyx Pearl"
Goodluck!