I am thinking of closing up a restroom at my school campus in order to enlarge the room next to it. I want to know approximately how much would it be to close up all the pipes and anything dealing with water. Its going to become a music room. There are 4 toilets and 3 urinals. There is also a sink about 20 ft. thank you for the help.

Not sure how much it would be but have you considered any code implications with doing this? There is a minimum requirement for the number of toilets and sinks a buildng is supposed to have.

In what country?

All commercial buildings have to have a minimum amount of facilities in this country. Educational buildings need 1 toilet and sink for every 50 occupants, there is 1 occupant for every 20 square feet. So if you take your total square footage and divide it by 20 you will get your occupant load, then you can determine how many toilet and sinks your building should have by dividing that number by 50. Your probably covered but it would be worth checking before you rip those out and cap all the plumbing lines.