Hello castleking!
You have not to take down ceiling.Price for that job could be from 10 to 40Pounds to install each point(depends of area you living) and cost of materials, but you have to know that downlighters in most cases should be fire rated or covered with downligt covers(Buildings regulations).
Best way for you-post job on this website and you'll get quotes from professionals.It will be free.Or you can get a quote after an electrician visit your home.
Please remember, if it's special location(kitchen, bathroom etc.), electrician must be part 'P' approved .