Is it possible to buy a Mac Mini with 750gb 7200rpm drive for $750 and use that as a "cost effective" 750gb Thunderbolt external hard drive in target mode?
Yes, but that will consume more power than a simple external HDD and as that is a 2.5" HDD, albeit with 7200 RPM, the speed gain is not really that much compared to Firewire 800.
Firewire 800 offers up to 75 MB/s read and write speeds, the 2.5" HDD will offer 100 MB/s. While that is 25 MB/s faster, is it really needed?
Is it possible to buy a Mac Mini with 750gb 7200rpm drive for $750 and use that as a "cost effective" 750gb Thunderbolt external hard drive in target mode?