With a budget of 4K I asked 3 plumbers for an estimate on a bathroom refurb, giving all 3 clear plans. I got 3.5K 3.2K and 2.2K. I went with the cheapest and thought that even if he went a bit over, it would be well under budget. Job finished I received an invoice for 5K. I asked why he hadn’t said during the job that it was going way over his estimate and he just apologised and said he had no way of knowing until he added it up at the end! What do I do?