Student version is $99.

If you can't manage to get Matlab, try Octave.  It's free and almost  completely compatible with Matlab. See http://terpconnect.umd.edu/~toh/spectrum/SignalArithmetic.html#Octave

I hope i can get something with octave, thank you.

You can also try R language. It is free.

You may get the student version free from the following link.

http://www.mathworks.com/academia/students.html