Ventilation Box - 2000 S40 Turbo

[sambham]

I was wondering the average cost to replace the Ventilation Box in a 2000 S40 Turbo? I am debating on whether or not to even fix it as the car is 10 years old and has 150k miles. I was given one quote of $475.
The exhaust began smoking the other day and had a burning smell. I am hoping this new box will fix the issue and I can get another year out of the car. I take very good care of it and maintenance regularly. Any help would be greatly appreciated.