Here are a couple of low cost choices- The Chinese one in the box looks to be an air motor with air cylinder to drop it down. The one made in California is semi manual but low cost and adaptable to a lot of machines. I would go with the California unit.
Milling Machine Accessory Air Power Drawbar A T Ant 300V R8 NMTB30 or NMTB40 | eBay
Power Draw Bar Fits Bridgeport J Head Milling Machines | eBay