Since your getting the runaround from other members, I'll answer your questions. By the time Pakistan gets the J-20 or J-31, being around the mid-to-late 2020s, budget permitting, India will also have inducted the much maligned and problematic, but still on scheduled, FGFA, which is the joint Indian-Russian fifth-gen project based on Russia's T-50 fifth-gen fighter. It's basically a stealthy, more powerful and maneuverable and better armed SU-27. It's a beast. Each of these aircraft, the J-31, J-20, and T-50 are expected to cost in the range of 65-80 million USD, so slightly less expensive than the F-35, who's price is dropping and will stabilize around the 70-80 million USD range. I hope this answers your two questions, the one about India's defenses and the other about the cost of the Chinese aircraft for Pakistan. I will answer additional questions if requested or needed.
India is also investing in surface-to-air missiles, ground and air radars (AWACS and IRS) and additional upgrades to its existing systems to ensure they can meet its operational requirements, one of which is to direct and and vector countermeasure to stealth aircraft.