If you are fairly handy with the tools then you will definately be able to get the job done for less than £1150.

My advice would be to cut out the ceiling where the pipe has been damaged and make the pipe good again.

I know for certian that the plasterboard for a area that size would be less than £150, I would recomend that you use 12mm board as it will help with sound deadning. You could go to the lengths of foil backed board as it will help with heat insulation - but it will cost a lot more.

I would strongly advise that you pay someone to plaster the cieling as it is an art in itself. Ceiling would rughly cost £300-350 to plaster and that will be going through a company, hopefully you may know someone 'from the pub' that may be able to do it at night for a bit cheaper?

Then decorating is up to you? paper the ceiling/piant the ceiling/ up to you but i'm sure you could do that yourself.

This should leave you with a nice bit of cash in your pocket for the bathroom!

BUT i must warn you that it is an extremely mess job when you rip a ceiling down as all of the dust, insulation and sh*t that has been between the boards will come down. I advise that you do this at a weekend when you can open as many doors and windows in the room as possible! also i would advise that you tape as many doors and openings between rooms up as possible to stop all of the dust transfering through rooms.