Believe it or not, it is possible to travel cheaply or free in the United States. By using community rideshare sites and boards and relinquishing some control, you can enjoy new sites and cities for very little or no money while meeting new people.
Register on CouchSurfing.org and eRideShare.com. Save time in later steps by preregistering on these useful sites.
Choose destinations. Of course, your final destination may be the same as your start point, but split your trip into one or more smaller legs. If you are starting in Minneapolis, for example, and your final destination is San Diego, choose points of interest in between, such as Billings, Portland and San Francisco. Increasing the legs of your trip will add interest to your experience and probably make it easier to find rides or ridesharers.
Find rides for each leg. If you really want to make the trip free, you will sacrifice some of your control over where you go and how long it takes to get there. Use rideshare sites such as craigslist and eRideShare to look up offered rides to destinations for each leg of your trip. You can also post a request for a ride to a destination on these sites. Also try community rideshare boards, often posted at college campus student union centers. If you have a car and are offering rides, make it clear in your ad that you expect riders to pay for gas.
Discuss logistics. Prior to the ride, make sure your ride provider or riders are okay with you not paying for gas. Often, drivers expect riders to pitch in gas money. If you are willing to, bring along the maximum number of riders (by contacting them through their ads) so that splitting gas will decrease the cost for everyone. If you are determined not to pay, offer to take the night-driving shifts or share snacks with the group. When payment or non-payment is agreed upon by all parties, talk about how long you want the drive to take: Will you drive nonstop to your destination? Will you camp or stay in cities along the way?
Stay for free. When you reach your destinations at various legs of your road trip, or if you have to stop along the way to rest with your riders/drivers, plan ahead by using CouchSurfing.org. You can find hosts to put you up for various stay lengths, as long as you are registered beforehand on the site. If you choose to camp, most legal camping sites will cost money, though some state parks offer free camp sites to hikers and bikers without RVs, so inquire ahead of time.
Pack. Bring only one change of clothing and a few extra pairs of underwear. Your rideshares most likely have very limited space, so pack only what you absolutely need. If you must bring camping gear, bring only the bare minimum of a sleeping bag, sleeping pad and tarp. Bring foods that are nonperishable and high in nutrition, like non-hydrogenated peanut butter, whole grain bread or crackers and unsalted fruit and nut mixes. Bring a refillable water bottle as well. You will need to obtain more food throughout your trip, so don't try to pack enough to last the whole time.
Eat and entertain yourself cost-free. Obviously, if you are road tripping to camp, you will be entertaining yourself in nature. In cities, there are many ways to enjoy new places for free. Ahead of time, using guidebooks and the Internet, look up free museum days, parks and gardens and free concerts. Libraries always offer guest passes to use the Internet, so start at one to find free entertainment in the city you find yourself in.