Hello,
Seems like we have had similar car quandries.......twice I have looked at Boxsters and then chosen Z4s...... as another forum member said, a cheap Z4 will be a safer bet than a cheap Boxster (I saw some absolute sheds in my price range).....if you do go for the Boxtser, read up on the bearing issue and the nikasil issue.....
I think £3k for a 3.0 is wishful thinking, but good luck with the hunt.
Cheers
Ben