How does a baby shower cost the parents money? Every one I've ever been to has been a) Organized by someone other than the parents-to-be and b) Wildly successful in terms of ROI.
I would say you would have been correct several years ago but there are many social dynamics going on these days.
For one the baby boomers (parents of soon to be parents) have large financial burdens themselves. They may want to help but lack the funds to do so and/or time (because they haven't retired yet themselves and might even be taking care of their parents).
Second people are having kids much later. I am 35 almost 36 and most of my friends and family are now geographically disparate.
Combined with above and the modern-busy-self-consumed-technology era we live in you seriously cannot rely on anyone organizing an event for you.
I don't blame this on my friends and family. It is just a reality.
Furthermore the expectation and cost to host an event has become far greater over the years.
Maybe it varies for people, but I've usually seen a good friend step in, rent out a spot at a park, get some tablecloths and balloons and things to snack on. They're also starting to be more co-ed, too. If you go all out, maybe $100-$200.
Source: Parent of 3 kids, uncle to 4 more.