When hiking I always wear lightweight nylon pants with legs that zip off to convert my pants to shorts whenever I desire. A new pair can look semi-stylish enough for city use, but there's enough variation in cut and fit that you'd want to try them on and have a good look at how they fit you.

The other thing to look for, especially if you go for a cheaper pair of 'convertible' pants, is whether the zippers around your thighs chaff or rub. These should be entirely shielded by a flap of cloth that keeps each zipper away from your skin.

Such pants can often be found on sale. Prices can vary from $25 up $90, depending on brand and features.