There's the ASRock PAUL:
https://www.asrockrack.com/general/productdetail.asp?Model=P...I have one, it works. Look at that board though! Given that component and board density, I don't find it very surprising that it costs around 200$ USD. Maybe you could get clever and design one that tries to work 100% via pcie device functions, and cut down the (physical) complexity of the IPMI device, but then the wide system and interface compatibility of the IPMI board would suffer.
To wit, the card needs to do the following, at a minimum:
1. Provide a VGA/UEFI/VFB-equivalent framebuffer for display capture
2. Provide a USB-device interface to emulate keyboard+mouse.
3. Provide a network interface of some sort for remote control
4. Provide GPIO headers/sinks at the appropriate power levels to replace traditional motherboard front-of-device switches -or- provide a PMBus header to perform equivalent functions with a support PSU.
You can get away with a subset of the above, but without that, you will be missing something critical to enabling lights-out-management. On top of that, a full-featured IPMI board is also generally expected to provide some fashion of environmental monitoring and fan control, which the PAUL does provide. It throws in some extra features as well, and provides some maintenance/lifecycle management capabilities of the board itself.
Providing all the above, is about the same amount of complexity of shipping a SBC and ecosystem itself, made moreso by the compatibility requirements.
You don't have nearly as big a market willing to pay $200 for all that -- its certainly not a matter of adding the chip and flash and dropping some vias.
Even having a standardish system-on-chip and non-bespoke firmware is 'new' (post-2020?). It could have been done 10-15 years ago sure, but noone was willing to do the long tail of tasks needed to get a product to market yet.