How much budget per day?

It's my first time to visit Japan and i'll be staying with my nephew in Saitama Ken area. Which places are the best to visit during my two week stay? On a tight budget, how much should i allot per day for rail fare, meals outside the house, some souvernirs? thanks for your reply.

Which places are the best to visit during my two week stay?

I recommend to visit places which interest you and which are recommended by your nephew (assuming he has been living in Saitama for a while):
http://www.japan-guide.com/e/e623a.html

On a tight budget, how much should i allot per day for rail fare, meals outside the house, some souvernirs?

Transportation obviously entirely depends on where you plan to go and where in Saitama you are located. For example, from southern Saitama to central Tokyo, a round trip by train costs costs about 1000 yen. From northern Saitama it costs about 3000 yen.

Some basic information about travel budgets:
http://www.japan-guide.com/e/e2410.html