ETL is not the biggest problem, but it is very time consuming, tedious, and costly because the tools overall suck. That is why I started Datalanche although to be fair we so far only solve part of the problem (storage, query, sharing).
Anyway the OP wants to learn how to do big data and make money. Well even if you are doing the cool stuff such as analytics, you still need to know ETL basics. I offered to give some experience doing that.