The bath will require complete plumbing & likely an ejector pump to pump the waste water up to your sewer line.

"If you have a basement or crawlspace, it will generally cost less than if you have a concrete slab foundation that has to be cut through. A basic bathroom addition can cost from $10,000.00 to $25,000.00. Depending on the job and location, a plumber can cost from $45.00 to $150.00 an hour."

http://www.homeadvisor.com/cost/bathrooms/