A Rental agreement is usually signed between the Lessor (landlord) and Lessee ( tentant) for a immovable property which the lessee has agreed to all terms of the Lessor and also the rent payable details are noted in this agreement.
As per Section 17 in the Registration Act 1908, it is mandatory to register for rent of immovable property from. year-to-year or for any term beyond 1 year or 12 months.
In normal practice, usually all rental agreements are signed for 11 months and mutually agreed to renew the same. If a rental agreement is for a period less than 12 months, then you do not have the need to register it.
However, it is always advisable to register a long term rental agreement as its protects the interest of the lessee and the lessor to any kind of a dispute in future.
The registration charges of the rental agreement varies from state to state, please check the state registration department site to get latest charges.
Generally, the registration charges for registering the rental agreement are borne by the Lessee.
Conclusion, it all depends on how you draft the agreement and in most cases it can be avoided.