Well if they have a problem with battery usage as a cost concern then they shouldn't be getting into a darkroom.
You can pick up an old enlarger for real cheap on eBay or maybe a yardsale in your town. But then they have to keep purchasing expendables like paper, chemicals, film etc.
When they sit down and do the math I'm sure a good set of rechargables and a charger will be a lot cheaper for them in the long run.
Maybe not as much fun for you tho. I sit in front of a computer all day, the last thing I want to do is sit in front of it at night playing with PhotoShop.