Building your own is a lot cheaper in materials IF you are very handy with tools and have the time to work out the kinks in the design. A wood feeder like Stinky Acres made will do the job if kept under cover and dry. Might have some chewing on it but just patch it up if they do.
If you want to to put the feeder outside you will need to purchase a metal feeder and place it facing away from the prevailing winds/storm path. To defeat squirrels you will need a heavy lid or a heavy spring tension on the doors. The majority of treadle feeders use the guillotine style lid, going up and down, and the manufactured ones have to use a light weight lid to prevent too many crushed chickens. We never went down that road, preferring the much safer inward swinging door and it needs two strong springs to put enough tension on the door that a squirrel or two cannot push the door open.
If you had a lot of squirrels, they might learn to push the door open but they will wind up trapped behind the door. Just lift the feeder off the mounting cleat, pour the feed out into a bag or bucket, then either take the squirrels for a ten mile road trip, put an exhaust hose down into the feeder and close the lid, or set the entire thing in a barrel of water for a half hour. Then shake the stupid tree rats out into the garbage. It rarely happens twice.
