$100 - $200, as used. On CList so you dont have to ship it. Or on one of the many Celica forums, so someone who wants it can do a local-pickup from you.
If it's been modified or had any damage from an accident (you found it in on a wrecked car), its probably less desirable
Do you know how many miles are on it?
Is the system inside the can still good, or is it rusted out?
Are there any rust spots on the exterior of it?
What does the tip look like? Scraped or scratches or swirl marks from being too aggressively cleaned?
Is the tip still shiny or is it golden yellow / blue.
The more information you can stick on your ad, the more likely you'll make as much back on your find as possible. Congrats!