CTHackATAHon has a fully refundable fees of INR 250 / USD 5. The fees is just a token amount to ensure serious registrations.
If you would like to have access to the conference as well, you can opt-in for the combo ticket which comes at a nominal cost of INR 1500 / USD 20 (This ticket includes CTHackATAHon registration and full access to #doppa2020)