Amazon is selling the Greenlee Textron #DTAP1/4-20 1/4-20 Hex/Tap Bit for $3.98 right now.
I hadn’t noticed these tools before — the Greenlee Hex/Tap Bits are combined drills with taps and a countersink with a hexagonal shank to fit in a drill/driver. You can read the .pdf for full details. The bit drills the proper-size tap hole, then taps the thread and chamfers the hole. The only thing that puzzles us is that they are rated for 10 ga. metal only, which seems thin given that the range of sizes goes up to 5/16-18′. With a 1/4″-20 tpi you would only get about two threads of engagement in metal that thin. We can’t see any reason they wouldn’t work in thicker metal, so it’s somewhat puzzling. It does seem like the sort of tool that would speed up fabrication projects.