It's 25€ on steam, both include all the expansions
30 on Switch is not steep
For perspective, though, even as soon as it came out of Early Access on PC, Prison Architect was routinely discounted by 75% so the perceived baseline for its cost is much lower. To be clear, it's a great game and nobody should have concerns about value for money in terms of hours-per-dollar, but when you consider everything from UI/controls to performance even before you look at the price, I would be cautious about recommending it on the Switch for anyone with access to a PC until we hear more about port quality, controls, and so on. It's worth $30, and better value than many games that are similarly priced, but the reality is that nobody who gets into it on Steam actually pays that much.
I myself have made a near-total conversion from the PC to the Switch as a primary platform, as I simply put more time into games that way, so I understand if the Switch really does add that much value for a player who wants to buy the game there instead. And some builder-oriented games that seemed designed first and foremost for a mouse and keyboard (I'm looking at you, Stardew Valley) actually turned out to be even better with controller inputs on a handheld, to my surprise. But it's only responsible to inform those interested in Prison Architect that the version on the lead platform, PC, is routinely available at $7.49 multiple times a year, every year.