What discount is appropriate for a job that ran way over schedule?

I hired a cabinet contractor to do kitchen, bath and utility room cabinets for my home. I was told the job would take around 4 weeks to complete, maybe a little longer. Everything that could go wrong did. My building contractor split on me and the cabinet contractor had a falling out with his partner. He got a new carpenter to work my job, but he had personal problems and left so he subcontracted it out to another cabinet builder. That builder took his time to finish the job. My job wasn't a priority for him. It took about a year to finish the basic cabinets and about 23 months to finish the entire job, redoing some that were poor quality. The job looks decent, maybe C quality, but there are flaws. The guy who I contracted with feels bad and told me to pay whatever I feel on the balance. The total cost was $32K and I owe him $3300. What do you think is an appropriate discount on the job?