Thought the RRP was a bit barmy, until I looked around and found this is selling elsewhere for: -
B&H Photo-Video USA £288.76
BT Shop £361.65
Developed togeteher with the Canon EOS-3 camera to boost its motor drive performance and attain maximum shooting speed, Canon's Power Drive Booster PB-E2 has been uniquely designed with a comfortable grip and controls for horizontal and vertical shooting. While most effective with the Canon EOS-1v and EOS-3, it can be attached to the EOS-1 and EOS-1N cameras.
With shooting speeds of up to 7 fps (10 fps for the EOS-1V). It offers 2 gear trains, Hi/Lo and adds a powerful third motor dedicated to a high speed mirror and shutter control. When used with the optional Ni-MH battery pack NP-E2, the hi-speed gear train is automatically engagaed and provides shooting speeds with continuous AI Servo AF as fast as 7 fps with the EOS-3, and 9 fps with the EOS-1V and EOS-1v HS (10 fps with the EOS-1v in one shot AF or in manual focus modes.
The booster is fitted with various controls, including a shutter button, AE lock button, focusing point selection button, and FE lock/multi-spot metering button, Main Dial, and all button function on/off switch. The PB-E2 provides equal operating ease in the vertical or horizontal position.