I only wonder how she had a porche to begin with!
Well, from Chuck's pay packet in 2.22, we can assume that in the Chuck universe, spies make a pretty good living. We really haven't seen Sarah spending money on life's "necessities" such as a house, food, etc, so what else is she going to spend that accumulated wealth on? It's not much different than my own experience with deploying to a combat zone. I get a slight boost in pay with my combat pay package, but spend significantly less money while deployed. I've known soldiers who have saved upwards of $40-50k while deployed for a year.