A short, one-word name (ex. cat.com), and especially .com domains, will be pricy because simple titles have a lot of potential uses, meaning people probably already check them out on their own. If you are going after a registered .com domain, you will have to contact the current owner, and even then, prices could be high for misspellings and multiple word domains. In the past years, companies and individuals have settled for bizarre names, misspellings, and old tricks like adding “the” or “my” to the front; note, however, that this will also reduce domain performance.
Be extremely cautious while communicating with the owner. Even if you casually agree to buy the domain via email, the communication might be used against you in court as a legally-binding contract should you change your mind. Until you’re absolutely certain that you want to make a deal, agree to buy the domain provided that all the terms are agreeable. This will leave you an escape hatch if things go south.
Even if the term isn’t trademarked, don’t buy domains that are just a variation of another domain name. This means avoiding plurals if the singular is taken (mediatemple.net vs. mediatemples.net), hyphenating a phrase (media-temple.net), or adding “my” or some other preposition (mymediatemple.net). Alternately, you might consider buying these variations yourself and set them up so that if someone types one of the variations, they are redirected to your main site.