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Looks like the cheapest price around. Snap On sells a 3/4" drive that goes to 600 and that's about $800. I don't think you'll find a 1/2" drive that goes that high.
It might be expensive, never bought one, but have used a handfull.
Doubt that it would be found at a discount tool place like harbour freight. But I've been wrong onr other time.
Bob
They have one a little less expensive than this, but it is too new in their line-up for reviews.
This was was reviewed favorably (as long as you believe the reviews are truthful!)
you can build your own torque multiplier, see page 2 of this link http://www.motionpro.com/images/documents/08-0134.pdf the more final torque you need the longer adapter you use.
I have one for the fan nut on Robinson helicopters that is about 3 or 4 foot long, 1/2" X 1 1/2' bar stock. I welded a 3/4 inch male square drive that I cut off of an extension on one end and a 1/2 inch female square drive off of a 1/2 inch extension on the other end. I than stamped the formula on the bar so I didn't have to look it up every time I used it.
You can pick up Pronto (Stanley) or K&D 3/4" torque wrench on EBay at pretty good prices. Seen them going for new or slightly used for around $200-$300.