An experienced plumber should be able to tell you the cost of project, after asking few questions and listening to you. Or at least he can tell you the maximum cost. You can ask plumber the final price ahead or the amount of hours that the job takes. This way you have an estimate of the project cost. Have in mind that your best option is always a plumber who tells you the finished price before every thing. Even if it sounds expensive, it is the best price.