Getcha coupla pintle hinges and some laying-around wood and go to town. Amazon has a lotta choices
You could look at sailboat supply houses - they sell stuff for hanging rudders, etc. They have pintles and gudgeons [a bracket to receive the pintle]. Sailboat hardware typically doesn't come very cheap, though.
When I started woodworking, I didn't know squat. I have progressed in 30 years - now I do know squat.
If memory serves me correctly, I think Lee Valley/Veritas sells this item.
Also check Highland Hardware. I have seen it in their catalog.
If you look at offerings across the www, $250 to over $400 is the going price. You might find one around $200, but most are $250 - $275ish. There are plans to make your own from threaded pipe. With seat and hardware, that avenue is still like $100. I think if you want one, you'll just have to pay real money for it. Or cut and weld your own.