a330300,
I see you live in Fremont; so you know how bad traffic is on 880S all the way to San Jose, especially around the 237 interchange down in Milpitas, on a
rainy Monday morning. Or maybe the Sunol grade (nuff said)
If you think that's traffic from hell, it ian't nothing compared to Baltimore-Washington-Alexandria triangle, as it maybe
five times as worse as what you see in your backyard.
If your time is more valuable to you, $20 extra (is that per day?) could worth a million pain killers.

I don't know about the weekends (if that's when you'll be out there), but you don't want to take the chance. And try to change your return from IAD as well.
Good luck!
Jamester
Fellow Bay Area traffic hater