I'm tasked with providing fail over of our Exchange 2003 Server. Currently we're using Microsoft backup to backup the mail store nightly over the network to another machine. We currently use double take to mirror a database server and it seems like a reasonable solution for the exchange server but it is quite expensive and I'd need to dedicate a standby server for it. I've heard double take can sync to a VM, but I'm not on support with them anymore and I can't find much info on the subject.
My goals are (of course) to minimize cost and downtime. I'd love to use my double take backup server as a standby for multiple machines (it's got the space), but I don't know if it's possible. The maximum downtime I can afford is less then a day (my servers are on hardware support contracts, but hardware (drives, raid controllers, motherboards etc) still takes time to ship), so I'm not looking for immediate fail over, just the ability to smoothly transition to a backup machine in an emergency.
What have people used? What works well?