I made a list on the registrar who provide bulk domain registration discount, hope it's help for those who looking on register / renewals / transfer bulk domain.

Mydomain.com
Price: $5.95 (ICANN fee included)
Coupon code: htmli.info
Get bulk saving + 15% by using the coupon code

Godaddy.com
Price: $7.09 (ICANN fee included)
Price applicable to more than 201 domains and above

Dynadot.com
Price: $7.50 (ICANN fee included, .com price )
Prefund $500 to get bulk saving

That's all I can find at this stage, will keep update in future. Hope the list is useful for you. Enjoy your saving.