Repairing a Leaky Pipe
Like a leaky faucet, a leaky pipe under the sink often can be addressed without calling a professional. Generally, you just need a new washer or nut, but in some cases the entire p-trap (the curved section) has to be replaced.
The parts should be $5 to $15 at a local hardware store, depending if they’re plastic or metal. Be sure to turn off the water flowing to the sink before taking anything apart.