How much it costs for chemical castration?

Go with the surgical castration.  It's cheaper because you can just have a friend do it after a couple shots of tequila.  

Chemical castration is only temporary and primarily used for sexual criminals.

If you did in fact have a medical reason for it, then your doctor would work with you on that. If you're wanting it done just because, then no doctor will perform an orchiectomy without a therapist signing off on it.

What exactly is your reason for wanting to lose your testicles?

On prescription the medication is not expensive, but an ethical doctor would not prescribe it unless you had cancer etc.