For my 986 it was around £315 for the year from Locktons, annual mileage 5k. That included PCGB Membership (which I probably would have joined anyway). Plus UK & Euro breakdown cover. Add those two together (£70 + £70 ?), that makes it about £175 for the actual insurance.
My current broker is Elephant (for my everyday car) and of course, they transfer you to Admiral Multi Car, as you cant have two cars with Elephant. They quoted £370 for the Boxster, with no added benefits.
I gave my local A-Plan broker a go as well and after about an hour they rang back with "a really special deal" of £550 !!!!