Here is an Ebay auction for a used Hipo counterweight by Ebay member "magmustangs" with a Buy-It-Now of $169.00:
1963-1967 Ford Mustang, GT, Shelby GT350, Cobra, Fairlane, 500. 289 HIPO CRANKSHAFT COUNTERWEIGHT-HATCHET. This is an ORIGINAL FORD PART. Removed from a 67 Shelby Mustang GT350 with 289 Hipo. . The Counterweight is in Great Original Condition. I have left it in as found condition. It has a little surface stuff but No Metal Pitting or Heavy Rust. It will clean up to look very nice. No cracks or splits. Not bent or damaged. Overall, this is a Great Original 289 HIPO Crank Counterweight.. Impossible To Find Original.