If you are looking to resiter a domain with .lk Extension , then here is the basic information for you. there are lots of Domain resellers providing .lk domain registration service with nic.lk approval.

of course, Read .lk domain registration Policy here Instruction found here
If everything okay here is the basic informations.

(CAT1) Registration Fee 5,000 + 12% VAT ( Including available second level domains )
(CAT2) Registration Fee 3,000 + 12% VAT ( Top Level domain only )

You can register domains via online nic.lk or any other .lk registry agents . Authorized agents details ound here

for more information check nic.lk or ask your friend google !