Contractor wanted to change price after completing the job

[Val J.]

I have a guy that has done a few jobs for me and we've not had any issues. I recently needed a roof replaced. Asked him for his bid and he sent me his quote via text. Afterwards We agree on color, date, time etc.  He asked for a $ to purchase supplies. I paid him and informed him that I would be keeping both of us accountable of the balances via text.  After the initial deposit, I send him an accounting of what was given and the current balance owed by me . No problems. When  he finishes the job he informs me that it cost more that what he initially thought and wanted $200 additional dollars. I stated to him that I believed it was his responsibility to price the materials &  labor BEFORE the job began so I could've at that time agreed or found someone else. I told him that I would go broke if I agreed to pay contractors more $ after a job was completed because the materials cost more or whatever. Anyone ever faced this issue. Did you pay or walk away?