I've had good experiences with PCB-Pool with RF boards of up to six layers. Their prices and deliveries are pretty good.
They are 'kicad aware', but their best rates are when the design files are submitted in GC-Prevue *.GWK format, as it reduces ambiguities and thus the risk of expensive errors. I see the use of Gerbers as a useful part of the checking process, not a bind, BTW. Chris Bartram
