If you're within driving distance, on a budget, and enjoy the outdoors, a national park (or state or regional park) can be an ideal summer bargain destination. Accommodations are as cheap as you'll find them (though you'll have to pack your own bed ... or sleeping bag) and you'll be surrounded by free activities like hiking, bird watching, and swimming. If everything but the sleeping on the ground sounds good, you can forgo the camping in favor of an in- or out-of-park hotel or motel. However, unless you're planning on staying at one of the no-reservations campgrounds in a park, don't wait until the last minute to book your accommodations; this bargain option is one many summer travelers will likely take advantage of this season.
Not sold yet? Here are some numbers that illustrate the sorts of vacation costs you can expect at national parks. At Yellowstone, for example, the entrance fee (good for up to six people) is just $25. Campsites for up to four people range between $12 and $25 per night. And early summer room rates near the park start at $59 per night. If you're not within road-trip distance of the park, you might consider flying into Salt Lake City, where you'll be able to take advantage of U.S. summer airfare sales from many major airlines. For more tips, Priceline.com blogger Brian Ek has a detailed and money-saving post on the best way to visit Yellowstone on a budget.
Other parks offer similarly good value. In Yosemite, you'll pay $20 per car and $14 to $20 for a campsite. And at Great Smoky Mountains National Park, entrance is free and campsites cost between $14 and $23 per night.