Trip to Yogyakarta (Jakarta)

Hello there! I'm a civil engineer from the Philippines and currently deployed here in Cikarang. I'm planning to go to Yogyakarta this coming Dec 4-6. Due to my tight budget and schedule, I will go by train only. Can someone please recommend me a cheap overnight accommodation and car rental service there? Or is there anyone up for some adventure and interested to join me? I'd be glad to hear and meet anyone. Thanks a lot!