Willing to Pay for Advice: Multisite setup

Hi,
I have 2 trixbox setup at two sites. they are using iax to connect the two system together.
I was hoping someone could give me some suggestions on the ideal failover setup.

we have 2 identical servers setup at each site.
each site is setup for its office. iax ties the two boxes together so they and dial over iax to the other site via extensions.

I want to be able to set it up so that if one server goes down the other server takes the load from the down office. i am not against move all phones to connect to one office server and setting up the other server as a backup. Just want to make it so we have some type of failover.

Please let me know what you would charge to give me some advice on this setup. Need to know if you have deployed something similar to this before.

thanks!