Harbor Freight sells a low cost set of LH drill bits. I'd do like suggested earlier and center punch the broken screw and then start drilling. Use the smallest bit and then work up in size one step at a time. It's extremely critical to stay centered in the screw you are drilling. If you are not centered work the bit sideways until you are. As the screw becomes a shell so to speak it will most likely spin out. And whatever you do don't use an ez-out. They are extremely easy to break off unless you are familiar with them, and once broken off you are going to be in a world of hurt.