It depends on what you call cheap..
Robot Electronics do a fabulous range of IP IO boards that can have their IOs mapped to each other via TCP.
They also have advanced DScript programmable boards that are incredibly flexible.
For example - https://robot-electronics.co.uk/products/relay-modules/ethernet-relay/ds1242.html
I’ve programmed one of these to respond to various UDP packets from OH to hammer out a range of bell chimes.
(This is the development UI that nobody ever looks at, as the chimer is triggered by UDP)
Or two of these Velbus modules can be mapped to each others IOs, but they aren’t IP, so they’d need a link cable.