Westworld cost a shedload to make
Add in the fact that Westerns are notoriously expensive (and HBO has gone way over budget on the genre before with Deadwood) and you can begin to guess at the costs but you're probably still way under. The word is the entire first season cost a staggering $100 million. As for the huge scale pilot- it could be as high as $25 million on its own. That included several delays and reshoots.
Now a lot of those initial costs will go down because items like the sets, costumes and props now exist, and there's also a lot to set up in that first episode. But HBO has a habit of going even bigger as time goes on and it's safe to bet that Westworld is going to continue in that way.
