It's easy to purchase a vehicle, but buying a car the sensible way takes a little more effort. Whether you're looking for a new or used auto, at a dealership or from an owner, here are some ideas to make your auto purchase as painless as possible. Set a budget Before you go shopping, figure out exactly how much you can afford. This is the most important part of the process. After all, car payments are a big financial commitment. Consider all your current monthly expenses, including your mortgage, utilities, food, childcare, entertainment, and tuition. Be realistic and make sure…