I usually don't hire contractors if the repair is something simple.  In this case, it would have been a bit of a pain since we have a pedestal sink very close to the wall.  We decided not to buy a new sink stopper assembly, instead we bought a metal mesh strainer for the sink which is easily removable, and bought a rubber stopper for when we need to fill the sink with water.  Sure beats paying a plumber or trying to be a contortionist to repair it lol.