It still depends where you are in Paris, there is areas where you can eat really cheap street food (the stands are illegal and aren't certified by health authorities, so it's at your own risks, and it's in areas some would consider 'unsafe').

Ten years ago you had more opportunities to eat different street food in Paris. Now it's kebab, and that's it. According to my father, 35 years ago it was great however. You had hot dogs, galettes, street pizza, barbecue, Chinese food and a lot of other stuff really cheap.