I bought a seeder last year so I could plant using my garden
tractor. The seed plates are $40 a piece, and only available in a few sizes.
I dug out some scrap plywood that was the same thickness as the plates, cut out circles, and carved them to fit. One is already customized to fit the field peas I planted as a cover crop. 3 more are waiting for me to decide what seed to use them for.
$160 worth of seed plates, for a piece of scrap wood and some careful carving.
(Now you're inspiring me to think about wooden gears and all the things they could be used for)