If I may mention something here, it would be TimeCamp - Free Time Tracking Software since few last month. My colleague recommended it to me, because I was looking for an inexpensive but reliable and rich equipped time tracking software.
It has all the features I needed - budgeting, invoicing, detailed reports creating. Now my company works the way I wanted!
I think all the people who are searching for a nice support should give TimeCamp a try.
I would rather recommend to hire a team of professionals and develop a good plumbing business software that will satisfy all need of your company. You see, if you choose something non-personalized it would never become profitable because it won`t be unique. I know what I am talking about because I have been through such conditions.