HA (High Availability) Failover Cluster in 2012 R2 Hyper-V is free?

The short answer is yes, but a failover cluster implies you have more than just a couple Hyper-V hosts. You need shared storage as well, e.g. SAN.

MO

We do have an SAN. But even we have only two pretty powerful hosts with plenty of resources, still not good for failover cluster?

That's fine. You only need 2 hosts + shared storage.

MO

Can I have one more quick question please, regarding Hyper-V Replica?
If we use shared storage -- SAN, and the replica server actually is physically located 100 miles away. In the event of primary host failure how can the replicated VMs (becomes in replica server -- 100 miles away from the SAN) access the SAN ?? That seems to be NOT feasible, correct?

The remote replica server would not access the local SAN that your two Hyper-V hosts running a failover cluster would be accessing. I'm assuming that the remote server is actually a 3rd server, not one of the 2 servers mentioned initially. If this is a 3rd server, you can run your 2 host failover cluster and then Hyper-V replicate that virtual environment to the 3rd server in the remote site. Hyper-V replication is free, but I wouldn't actually recommend using it. I would recommend using something like VEEAM backup & replication to do the replication. Better disk efficiency if you want to hold onto generations of your replicas.

MO

You said you wouldn't recommend using Hyper-V Replica since its disk lower efficiency, compared to commercial backup & replication software such as Veeam. Can you elaborate a little bit more about the reason why its lower disk efficiency?
Appreciated.