Webcams are cheap. Even camcorders can be had for under $500.
Mount them near a window, facing out.
Radio Shack says they sell two products that should help:
(1) a camera that connects to a VCR and records for 8 hours, for $119
(1) a camera that can film at night, connects to a computer and can record endlessly, for about $200.
When the vandalized office opens Monday, I will offer to donate something to them until the election is over.