The local body shop guys should know where to find the airbrush (or however they do it these days) artists. Chances are often good you might find someone who works out of their house or cellar who can do a heck of a job for not a lotta money.
The Triumph price seems Mighty high to me.
If you want to see an outstanding example of paint artistry on a Triumph, check out photos of Airguy's bike. His tailight setup is awesome too.