If you're looking for inexpensive (but nice) epaulet/uniform shirts, I would highly recommend Quartermaster's web site. I bought their Law Pro shirt to wear for piping gigs, and have been quite pleased with it - looks very professional and was comfortable even in the heat. (My first piping gig was playing at a Relay for Life in August - it was 99 degrees at 10 PM!)

Thrift stores and eBay are also good sources - I got a tweed jacket for about $20 from eBay and was able to turn it into a nice kilt jacket.