An inexpensive option is to buy a straightforward reflective vest and put that over your regular running jacket, shirt, or whatever. The Nathan Reflective Vest ($20) is that very animalit's extremely light, fits over just about anything, and has vertical and horizontal reflective stripes for ample illumination. Works very well.
The third choice is to use one of the above AND add a blinking light. Roadrunner Sports, among other places, sells armbands for $17 that have LED lights attached. That makes you actively visible from a great distance, regardless of whether or not a car's headlights are aimed at you.
And of course, it always makes the most sense to simply assume nobody sees you, and act accordingly. Run against trafficnot with itbe cautious, and obey all crosswalk laws. That'll keep you running in safety.