We have a leak .Plumber couldn't find,said we needed to get a leak detection business.They said it would cost an estimate of 2-$300.00 just to find leak, why is that? And I read on here they would find leak and then bared it and bag dirt what exactly do they do?What's this mean? We think it is under concrete slab? And does this charge including the leak finding and bared the pipe and bag the dirt? I think that's how I read it.Thanks...