“Leave to appeal a costs order will not be granted save in obvious cases where the party seeking leave convinces the court that there are strong grounds upon which the appellate court could find that the trial judge had erred in the exercise of his or her discretion: see Brad-Jay Investments Ltd. v. Szijjarto (2006), 2006 CanLII 42636 (ON CA), 218 O.A.C. 315 (C.A.), at para. 21. An appellate court should set aside a costs order only if the trial judge has made an error in principle or if the costs award is plainly wrong: see Hamilton v. Open Window Bakery Ltd., 2004 SCC 9 (CanLII), [2004] 1 S.C.R. 303, at para. 27.”