This can apply to any time of year, but make sure your vehicle is in proper running shape by checking your oil, tire pressure, antifreeze/coolant and other basics. Your trip will no longer be affordable if your car breaks down on the second day!
Try to make your plans for before Memorial Day, one of the biggest travel weekends of the year and the kick-off of warm-weather vacation season. Prices will jump at that point and availability at your top lodging choices will decrease.
Don't be afraid to try and negotiate over your lodging price if it's not high season yet. One ploy is inquiring about a two-night stay, mentioning that you'd consider staying longer if they could offer any kind of a special rate. They don't want to lose your business, and you have nothing to lose by asking.
If you're actually taking a weeklong vacation, look into a vacation rental as opposed to traditional hotel lodgings. This can especially save money if you're traveling with a group-three couples, for example, sharing a three-bedroom house for $2,000 is still cheaper than a good hotel.
Think about avoiding some of the more iconic spring destinations-such as Martha's Vineyard or Fort Lauderdale-which are more in-demand and thus able to charge more. Locales that don't really get busy until summertime (think the Coast of Maine for example) are often just as pretty in spring, less expensive and less crowded.
Spring is a time when there's usually plenty of fresh produce around and plenty of fish and game in season, so think about fixing your own meals, enjoying a picnic and other alternatives to expensive dining out. A farmers market is the perfect spot for finding fresh veggies, cheese, meat and other healthy edibles.
Bypass costly entertainment like theme parks and upscale golf courses for equally entertaining free or cheap fun. Spring festivals are a good choice, as is hiking at a great park or other outdoor venue. And when the spring rains come, look into museums (often free, rarely expensive), art galleries and the like.
If you don't mind roughing it a bit, consider a state or national park. These are undeniably some of the most scenic and naturally beautiful locales anywhere, and if you already have camping equipment handy, it doesn't get much cheaper than camping out. If not, consider a campground with tent cabins (such as KOA).