Bit of a 'horse bolted' reply, but I have an
USB/eSATA enclosure from Novatech which you can add your own Sata drive to. I stuck an old 160Gb drive in, but no reason you couldn't get a
WD 750Gb Caviar to use with it - slightly more (~£80) , but if the hdd mech dies you can replace it and it has the option to connect via eSata.