The most expensive aspect of traveling is not usually the airfare or the car rental or the admission tickets to local attractions. It's the fact that you will have to pay to have somewhere to sleep at the same time still keeping up with the payments on your mortgage or rent at home. Staying in different types of accommodations leads to drastically different types of vacations, so investigate all your options before you book. Here are some options grouped by affordability.
The most expensive way to travel is to book hotel rooms wherever you go. Hotels have many different price points from penthouse condos that cost thousands of dollars a night to no frills rooms you can book for less than a hundred bucks a night. You can get some great deals shopping online at the last minute on sites like Hotwire.com, but generally speaking staying in a hotel is your most expensive option, even if you're getting a special rate through AAA or for a lengthy stay.
If you're staying for longer than a few days, it's often worth your while financially to look into rentals rather than staying at hotels or resorts. Paying the rent on a condo or time share is hundreds of dollars a week rather than per day, so you could save a lot. You have to buy your own food and look after your own needs in a condo, but many people find this preferable to hefty restaurant bills and bland, samey hotel decor. Another cheaper option than a hotel is a motel or small inn, which is similar but not as upscale.
The reason for the high cost of most hotel stays is that you're getting a full range of services. However if you're content to mostly look after yourself and you don't need the anonymity of a giant tower full of other guests, you might choose a bed and breakfast over a hotel. Staying at a bed and breakfast is just one step removed from staying at someone's house. You will likely have to chat with the proprietor over breakfast and share a bathroom with the other guests.
If you're trying to keep your budget to the absolute minimum, it is possible to get the accommodations line on your travel budget down to zero. Look up old high school friends or relatives who now own condominiums and ask to stay with them. Or, if you don't know anyone where you're going, register for a website like CouchSurfing.com and meet some people online who are willing to come have you stay. Though they won't require payment, it's only polite to bring some sort of gift.