Check Ebay for an old John Deere 71 Flexi Planter. These are pretty much the state of the art in terms of old style mechanical planters. In fact they are so good that they are still made today (but no longer made by Deere). The beauty of them is that they are SIMPLE. So simple that I can even figure out how to use them. The planter plates are available and inexpensive. They can be adapted to plant all sorts of seeds. And the used/refurbished units are reasonably inexpensive.
Very nicely refurbished 2 row units, with custom box steel 3pt hitch set ups are typically found from $700 to $850. At this price range, expect the unit to have been completely taken apart, gears or chains replaced as needed, sand blasted, primed and repainted, with correct decals, etc.
At the $400 to $600 price range you occasionally find 2 row units, the ones I've seen have lighter built (but still probably good enough) 3pt hitch assemblies, typically have been repainted, and they don't appear to have been totally rebuilt but still should be serviceable.
My 2 row unit is pictured below. Mine has large fiberblass hoppers, but honestly they are 10x bigger than I need. I'd be just has happy to have the standard steel hoppers on mine. It came this way so that is what I have. You can also find 1 row planters for sale on Ebay. The price for a 1 row unit is typically about 2/3rds the price of a 2 row unit.