A Cayman is on a 2 year service cycle, so when you take the £200-300 per year servicing on the Zed, the £500 for a Porsche Service Centre to service the Cayman isn't expensive at all.
Another example is disks and pads for the M6. BMW main dealer want the guts for £1200 for the fronts, the exact same OEM disks, pads and sensors on eBay are sub £500. BMW service costs are a joke, they quoted me £960 for a major service. Needless to say, the M6 goes elsewhere.