How much is repair cost for a leaky lawnmower which hit a metal pole in ground?

Groundhogs? Is that what you told your wife? I once set the mower down on a metal pipe that mom pounded in the ground to keep us kids from mowing into her peonies. It sheared off the woodruff key on the flywheel. But it didn't burn oil after I fixed the key. I think the prognosis for your mower isn't as good as mom's peonies. If it will run, limp along. If not, you might be able to fix it. Tear it apart and see what it takes. If you have the time, you might be able to fix it for less than a new one. I'm going to tell mom about the goundhogs.