I bought my coconut oil from Holland and Barrett. It's pretty pricey(around £15) but it's unrefined. And it was in a sale where you get 2 for 1. I know you can buy refined coconut oil from ASDA really cheap. But it's not as good.
I'm sorry I can't help you more. I have no idea about sealing or humectants. My brain has been overloaded with information it's just refusing to think now.
This is my prayer. That I'll die living just as free as my hair.