/jp/ - Otaku Culture

So /jp/, my friend and I are discussing spending the summer in Japan. Her parents have offered to pay for air fare and help her out once she gets there. However, at the moment our biggest concern is still money. I'd like to be able to plan out my budget and know exactly how much money I'm going to have to spend on this. Any tips on budgeting?
Also, any recommendations for cheap lodging and food? Other logistical cost stuff a first-time traveller should know (both of us have never travelled on our own)?
General tips for traveling in Japan thread, I guess.