Yup. It was more expensive for Valve because they have a custom chip. These other devices are using off-the-shelf chips, so it's a lot cheaper.
Look at the minipc market (e.g. minisforum), and then add a screen, battery, and build in a controller. It's really not a complicated product for a company that already makes similar devices, especially since they can probably reuse parts in other products.
Valve can go into the negative selling Decks, something that their competitors can't reasonably do because they will get money from Steam store sales made on the Deck. I for one went from buying 3-4 games a year to like a dozen because it's been so convenient.