Any favorite PC I/O for hobbiest?

Just wondering if there are any favorite I/O systems that are hobbyist
friendly.  Something like Ethernet I/O, ProfiBus, ModBus, DH+, RIO.  For
example I know I can get an Allen Bradley PLC reasonable on eBay but then I
need an expensive interface card, I just thought their could be a more
economical way I'm not aware of.

I know many of the HMI's can be used with many different brands of PLC's so
they evidently have drivers and hardware to communicate.  I thought someone
may have a good source for interface cards and drivers to work with I/O.

I'd like to play with writing PC software to do HMI and control functions.

Thanks!

RogerN