Surefire is the gold standard for shotgun lights. Period.
Their replacement fore-ends define the category. There are more ways to go about it, sometimes for less, but if it's for serious use, that is where I'd start looking.
MagPul's replacement fore-ends, when they start shipping, with a Fury in a LaRue LT707 mount would be my personal "other option" in performance/price. Many cheaper options, but most won't survive shotgun use.
"And Shepherds we shall be. For thee, my Lord for thee. Power hath descended forth from thy hand, that our feet may swiftly carry out thy command. So we shall flow a river forth to thee and teeming with souls shall it ever be. In nomine Patris, et fili, et Spiritus Sancti. Amen."