$300 is insane for a 2TB external hard drive. Especially since Thunderbolt adds no advantage for a standalone hard drive. No hard drive comes close to maxing out USB 3.0.
Sure portable drives are a little more expensive than regular but you can pickup 2TB portable USB 3.0 drives for $130. So that's an additional $170 for a Thunderbolt connection.
The only time Thunderbolt really adds an advantage would be for an SSD RAID of 2 or more SSD, ultra fast PCI-e SSD or numerous Hard Drives in RAID.