When you pay money for something (more than you thought?) and you don’t really want to. This phrase gives me an image of turning over soggy soil with a big garden fork, like spending the money is a big effort that really hurts. You usually only fork out for un-fun expensive things, like a new washing machine, travel insurance to America, or renewing a monthly travel card. It’s heavy work!
Fork out for something
The medial malleolus 