Cautionary tale! My Dad just paid $40 per esta by getting duped into using one of those disgusting esta web sites run by third parties. Make sure you've got the right link and pay the right price!!
He did a Google search. The site just basically asked him the standard questions but acted as an intermediary and charged stupid money for the privilege.
I just did ours for our trip via the link on our airlines website.
Did my mums for her trip to LA the same way.
First time I applied when you did not have to pay I did google it and got some really weird sites saying that they were official ones and wanting to charge you even though I knew at that point they were free.
Sorry your Dad got stung though its horrible when that happens.