I bought mine used for $120 and got myself a treat with another 'value lens' from canon. IMHO this is the best walkaround lens for street photography on a 1.6 crop SLR.
It is small, light, and very unobstrusive yet the pictures that you'll get are of good quality. the small profile of this lens makes it useful for documenting events, parties, street life & everyday activities without being typecasted as a pro. Its cheap price enables you to use it sparingly on any place or situation without worries of being mugged, stolen or damaged--it's more easily replaceable than an L prime. And the results? They're quite good & usable and sometimes even stunning.
On the build quality department, I would atest that this is one tough lens. One time, I was shooting a gig in a bar in manila, I accidentally dropped this lens from the height of five feet on a concrete floor. Fortunately, it hit the floor by the corner of the barrel at the mount end so the glass didn't break. It ended up having a dent on the lens mount. I tried it back on my 20d, it was a tight fit though, but voila, it still worked -- AF is still ok, images still sharp as before, and no unusual sounds or clicks from inside. Its performance is still good that even with the dent, I was still able to sell it when I sold my 20d.