The actual materials for something like this is very inexpensive. A roll of PLA filament is around $20 - and this uses about 10% of a spool. The costly part (along with the price of the printer) is the knowledge needed to properly use the machine. There is a very steep learning curve on making sure your printer gets you parts that are high quality. This is one of the main reasons people charge a lot for printed parts. It takes a lot of knowledge to get the printed part, a decent amount of time to make sure everything prints properly, and the opportunity cost of the machine being in use. This is all ignoring the good 5+ hours I spent painting them afterwards haha.
I actually wrote a book to help new people get into 3D printing if you (or they) were ever interested.
Thanks for the message!