Those bosphorus cruise boats charge 500-800 try for day passes. IETT bus 25E from Kabataş to Sarıyer covers the exact same european shore route for a standard 17 try istanbulkart fare

You dont get the annoying commentary but you do get to sit with actual istanbullular commuting to work. Plus buses run every 20 minutes instead of limited tourist boat schedules. The 25E hugs the bosphorus coastline past bebek, arnavutköy, and all those waterfront mansions the tour guides point at