cost depends on whether you are converting existing square footage into a bath or doing an addition to add a bath. Either way, you need a permit. You will be doing plumbing, electrical, and hvac work, so don't you want it inspected? I know everyone complains about the process and run around the city gives, but when you go to sell, the disclosure statement asks if there was any work that was not permitted, so you will have to disclose and this work will be more closely scrutinized. In addition to city inspection, you may want a private inspector to check the work. There are some great local contractors. ask on neighborhood facebook pages and message boards.