ESXi backup

I inherited a couple of VMware hosts running ESXi 5.0 and I'm looking for a free/cheap way to back them up at least weekly. I tried Veeam and Altaro but basically ran into the same issue: "ESXi version prohibits execution". Is there a way to backup the free version of ESXi? I'm pretty new working with VMware so maybe I don't really understand how it works. Could I just at least copy the vmdk files from the datastore without shutting down the servers so I can have a copy? The tech before me was just backing up at  file level but I would like to backup the VM entirely too if possible.