Honestly, you have some pretty decent lenses already. A nifty fifty, a tele, and another wide angle. @Teradore already listed some other good sigma options, but honestly with 500 euros, you might want to buy a new camera all together. You could easily buy an SL2 (200D), or a used full-frame camera.
If you don't want to replace your camera and decide against those two lenses (17-70 and 17-50), a nice all-around Sigma lens I have is the 18-250mm f/3.5-6.3. It's really good "tourist" lens, and is good for shoots like weddings as well because of the flexible focal length. I try to stay away from zooms for street shooting, tho.