The price for half marathons, and I'm sure this applies to full marathons, has skyrocketed over the last year or so.
Here's my theory on all of this, it's just a theory. Races, such as these, have become commodities that are bought and sold as products by for-profit companies. And with any product in a business, pricing strategies are developed to increase the bottom line - profit. Somebody, somewhere is making decisions regarding how much they think people will pay for their product.
Granted, there are expenses to put on a race. But with these prices they are not just concerned with covering those expenses, they are concerned with profit.
There are still some half marathons that are reasonably priced and I will search those out. Maybe I'll switch to doing more 5K races as they tend to be not for profit and in many cases, support a charitable cause.