I have one of the cheaper, wired computer (Sigma BC 1009) on each bike. The 1009 is an older model and is being replaced, so you might find them on sale. You’d need to buy 6, though.
The model 1609 (old) and 1612 (new) can be programmed for 2 different wheel sizes, so you could move the computer between two bikes. They are available either wired or wireless.
Just remember that swapping a wireless computer from bike to bike means that you need to move the computer on the handlebar, the transmitter on the fork, and the spoke magnet (which would be a PITA). And mounts and magnets usually don’t cost much less than a whole computer.
I’d recommend buying 6 cheap computers (like this)and just leaving them on the bikes. That would just be the least hassle, IMO.