Public transit from airport:
If you don't have a lot of luggage, taking public transportation to and from airport can mean big savings. train would cost very less.

Optimizing car rentals:
Car rentals can sometimes be most economical alternative. Between Washington Dulles Airport and Baltimore, renting a car was far less expensive than $100+ taxi or shuttle fare between those two cities. I often rent a car for one day at beginning and end of my trip for airport transportation and then plan my suburban meetings for those same days.

Off-hotel parking:
On my recent trip to Baltimore I saved $10 per night over hotel parking rates by parking in a garage down street. Plus some cities are more lenient than others about on-street parking, so it's always worth a troll in neighborhood around your hotel before deciding to pay to park.

Skip airplane:
In some areas of country, train is a viable alternative to air travel. Even with higher gasoline prices, for trips under 500 miles, it often makes more sense to drive especially when traveling to smaller cities where air fares are generally higher. And driving your own car eliminates air fares and rental car charges…as well as all hassles and aggravation of flying these days.