Firts time in Japan

hye, Im a backpacker or budget traveler. Im planning on my first time visit to japan and on a tight budget. I do some research on internet, I discovered that there are cheap transportation at the airport like bus, or railway like Keisei Limited Express. Maybe my question is a litte bit out of topic but any cheap accomondation like hostel or homestay in tokyo and karuizawa? Bacause I plan to stay in tokyo for 2 days and then off to Karuizawa and stay there for another 2 days before I leave Japan for Malaysia. Thanks for ur feedback! Domo arigatou!