If you plan on driving down yourself, there is plenty of parking space available at the temple complex. It is a 45-minute drive from central Jogjakarta. You can hire a taxi from the nearby city of Jogjakarta. It will cost you around 150,000 Rupiah each way, although the price can be negotiated. They are easily available for a day trip from hotels and local travel agents.
The best way to explore the Borobudur Temple complex is on foot. A toy train goes around the temple complex for a fee, but it is not very practical to do so. You could also rent a bicycle from nearby hotels or locals if you wish to explore areas around Borobudur.