DH-485 communication between ml1100 and ml1200

Can a ml 1100 communicate with a ml 1200 via DH-485 ?

And does someone know a cheap alternative to Factorytalk ?

The ML1100 has a serial port, and I do believe that you can configure it in the port settings as DH-485.
There are many ways to get the two talking together, but you have not indicated what the goal was, so this is the best I have for you currently.
What do you mean cheap alternative? Do you mean HMI software, or what?

You could buy a 1761-NET-ENI then your 1200 would be on the Ethernet and as SNK said the 1100 has Ethernet so you could have them both communicate on the Ethernet, not DH485 but you would still have comms

Do you have them both? if your 1200 has an R on the end it has two com ports and you may be able to configure the second for the NET-ENI