Depending on which model you or he wants, I have seen them for around $35 to $40 online. I think it was backcountry.com that had a few models in that price range. Other than that, I think your best bet is to find some local retailer, that has a coupon for % off and try to use that. I have noticed that some coupons specifically exclude certain brands, Keen usually being one of them.
Good luck! We own both Keen and Teva sandals and love both of them. I have open air Tevas that I absolutely love for everything, except where open toes are a problem. They are cooler and more comfortable to me than my Keens. But, my wife likes her Keens better. To each his own, they are both great!