The sale price of the house doesn't matter; it could sell for $100k or $900k, the builder is still out the $50k or more they paid out in fees. Which was most likely passed on to the buyer and I bet the mortgage companies have no complaint.
Its sounds like a big number until you consider the final cost, aka everything is relative, it would be a much bigger deal if the houses were selling for $100k because then it would be 50% of the cost.
They're basically forced to build a (relatively) big expensive house so that the final cost seems reasonable despite the $50k in fees buried in it. Hence why they aren't building entry-level priced houses - they're too cheap to hide the fixed fees.
Edit: there are no entry-level houses because zoned land in places where people want to live in the bay are is more expensive than a lot + house in most other places. There are lots selling for >$500k or some for just as much with tear-down houses on them. That's not due to the fees.
If $50k is 10%, that means it's a half million dollar house. That may not be much by comparison to housing stock in California, but there are very few places where that's considered "entry level."