Well, true enough. (You also save money on the taxi, if the alternative were taking one.) I just think there's a certain value to be attached to the bother of having the thing hired out with some random driving it while you're not around. I don't have an actual figure for what this value is, but my gut says that it's not sure airport parking is quite expensive enough to make up for it :)

I'd want to be at least certainly making a profit on the basic rental, no matter what happens. (But then again, it's probably unlikely that every renter will drive it 90 miles per day. Additionally, perhaps the free carwash and valet clean should swing me more than it does. And maybe I've just always visited airports with cheap parking. Etc.)

Realistically, I suppose, I've just made this decision somewhat irrationally, thinking of the bother and expense of sorting out a knackered clutch and a pile of parking tickets and a tank that's only half full (probably of the wrong type of fuel). But even after trying the more rational approach given in my original post, I'm not finding the figures to stack up well enough to convince my gut otherwise...

It's $18[1] to park at SFO. Assuming 4 days it's $40 vs. $-72, I'm not sure it would be worth $28/day to me to run the risk of damage to my car, tickets, etc. There is the upside of a carwash and not having to worry about damage in the lot.

If I'm travelling on business somebody is going to be picking up the cost of parking anyway.

[1] http://www.flysfo.com/web/page/parking/options/long-term/

yeah, at the bottom of the return receipt they actually give you a very rough estimate - long term airport parking for $18/day @ 10 days, + the $40 i received from flight car, add in the round-trip cost for a cab ~$100, and that's a +/- of $320. but, as to3m said and i had mentioned in my post, i don't know if it's worth the post-rental hassles as well as the added stress during your vacation - again, it was my choice, and i don't regret trying out the service