Hey brother u will get cheap hotels in hampi near mango tree restaurant but i suggest u to stay on hippies island where u can get tents in low cost and enjoy the night life of hampi
If you are traveling from Mumbai via Bus take the bus to Bangalore via Hubli, From Hubli you can either go via cab or Bus, but i will insist by booking a cab from Hubli to Hampi. Have a great time.
You can book a bus from redbus and if not, train is the preferred option. You will find so many options at a budget price to stay in Hampi on arrival. Get a boat to the hippie island and stay over there. The atmosphere is perfect for travellers out there.
Bus and train info can be found here - http://hampi.in/mumbai-to-hampi
Stay options are lot. If you want to pre-book, you have few listed under booking.com. There are just guest houses and shacks. Prefer to go there and book the stay. There is 2 side of Hampi - Anegudi, the silent side and the Hippie island- crowded one.