Have you tried Photo Technica here in Sydney? http://www.phototechnica.com.au/
I've never used them for anything other than 35mm but their pricelist (which you can download off their website) says that they can do E6, C41 and B&W processing of 5x7 for $8.36 ea.
Hope this helps. If you do end up using them, let us know how good their service is for LF processing.