How much does india charge an overseas visitors for gamma knife surgery?

While I do not. Know and googled it, gk was developed in the 1950's. Requires a neurosurgeon and radiation oncologist to identify the target lesion, define the adjcacent tissue tolerances, and deliver a single very large dose, typically 16 - 24 gy, depending on size to the 50% isodose line. Google says the price is frequently 20 -30% less than in the us. Charges are in the range of $25 - 35 k in the usa.
Ask the hospital. You should call the hospital in india and ask them. Call other hospital for price comparison.