Started the car today and it sounds like a boy racers dream, deep burble that on a bit of inspection is blowing from somewhere under the front

2003 3.0 v6 petrol engine, just done 122k miles. It’s going in Saturday but I’m hoping it’s nothing too serious, any common faults with these?

If if it’s a cat gone, what can I expect to pay and where do you suggest getting one from?

Fingers crossed it’s not...