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Yeah they use them for getting things like stuck drive shafts and things that need pulling out with a bit of wallop.
I have been on the look out for a heavy one, you’re right they are expensive although you could make one. It’s just a rod with a weight.
There are videos where people have made a frame that pulls the post out, they look pretty good and fairly simple to build if you have some suitable scrap steel floating around.
Can buy them easily enough. There’s a guy on YouTube who had success using one.