Cutting notch out of tile- least wasteful/ fastest option
How are you cutting all the other tiles? If I'm picturing this correctly you can't use a snap cutter for that type of cut.  If you going to purchase something for one cut I would get a handheld 4" tile saw ($50 - $80). Because the blade is 4" you can carefully do the 4" wide cut without going too wide. You can also use water with it to cut down on the dust, trying to keep it wet may require a helper though. Another option is to have the home improvement store do the two straight cuts and then make the 4" cut with a dremel tool with a diamond blade, that will go rather slow but you can get a cheap one with blades for less than $20.