1966 Ford Mustang 66 289 V8 Engine Recently Had Taken Shop Beacuse Would Smell

I have a 66 ford mustang with a 289 V8 engine recently I had taken it to a shop beacuse it would smell like gas as I would drive it , they said one of my cylinders was not working or it maybe broken, I was wondering what the cost would be to get that fixed or if It's just better for me to rebuild my engine and what would be the cost of that. I just want to get it in good running condition