I personally still use them for 3D printers, and Raspberry Pis still provide good performance for the price if you can get them at MSRP. At that 40$ price range

I personally still use them for 3D printers, and Raspberry Pis still provide good performance for the price if you can get them at MSRP. At that 40$ price range the main alternative is going to be an Allwinner H616 board like the BTT Pi or the Orange Pi Zero 2. I have actually run into a performance issue on one of my 3D printers that necessitated swapping a Pi 3 for a Pi 4, so performance did matter, and I'm unsure if a H616 would keep up. I do have a few boards that are faster than a Pi 4, such as the Radxa Rock5 with the Rockchip RK3588, but they cost way more than a Raspberry Pi (once again if you can find at MSRP).