You can't put a price on it. Imagine, for example, if when Donald Trump was signing up for Twitter, he got irked off and decided to use a different platform instead. That's potentially 60M people using your competitor. Poor user experience can decide the entire success or failure of your service or product.

People generally have too much tolerance because they've been programmed to accept bad user experience as normal. Services which require you to confirm an email are the typical example.

Imagine a door salesman came to your door, pitched you a product, but before you discussed any price or subscription, they ask "please can you go and get a shovel while I take a dump on your doorstep?" Well, that's the kind of experience people get online.