if you are thinking of bulky external burner better go for casing + a good burner. I have been using my external burner same way its good deal and will cost you less than 2K with best burn speeds @16x upto 22x. will need external power adapter which will come with casing. Any branded external burner using power adaptor will also cost more than 3.5K.
If not you are thinking of slim burners you can get LG/Sony slim burners which go with 8x burn speed. LG costs somewhere 3.5K and Sony somewhere 4.5K. running on using USB power
Also I had seen LG external burners which need a power adapter in Croma in @2K. Havent checked recently in Croma, but it was the best deal you can think for branded external burners