Hi Nishank, Japan is beautiful in Spring, here is a list of places you must not miss during that time:
Shinjuku, Tokyo: you just can not miss the Cherry blossoms of Tokyo if you are visiting in Spring time.
Fushimi-ku, Kyoto: Daigo-Ji Temple
Takayama, Gifu: Takayama Old Town
Sapporo, Hokkaido: Odori Park and Kawashimo Park
Yubetsu, Hokkaido: Kamiyubetsu Tulip Park
Hitachinaka, Ibaraki: Hitachi Seaside Park
During the time of Spring a lot of traditional festivals are being held all around Japan, so you must not miss them.
The expenditure will depend upon the places you are staying and the way you are travelling.