Personally, I've never found the "don't rent from the airport" advice to hold water. It might be true if you're just calling them up or booking straight through them online but there are loads of deals to be had through travel sites like priceline, mobissimo, kayak, etc. I typically rent a car a couple of times a year while traveling and every single time has been through an airport (or off-site shuttle) location, even when there were more convenient locations nearby, because they had the lowest rates. And I'm talking ~$17-23/day, major cities, unlimited mileage, mid or full-size, during holiday periods like New Years and spring break, and through companies like Avis, Enterprise, etc. One piece of advice I do have is to not try to pinch pennies because you won't get the deals. More often than not, while the advertised rate for a compact is supposed to be the cheapest, it isn't. It might be true on a day-to-day rental basis but typically the mid size is the cheapest for a weekly rate. Gas is almost a non-issue these days since most of the mid size fleet push mpg into the high 20's-30s, or nearly identical to an "econo" compact. And even when the compact is cheapest, it's usually only a few bucks less than the mid size and my legs like to breathe.
