As little as possible really. I'm fairly new to the whole flash thing so can you just confirm that I've got the right understanding of these terms?
Radio slave would involve attaching something to the camera which would wirelessly trigger the flash, attached to another 'something'?
Sync cord is attaching a hotshoe to the camera and one to the flash, then connecting them via a PC cable?
Infrared triggers would use an infrared sensor on the flash and then use the flash of the D80 to trigger it?
Am guessing out of all of these the sync cord is the cheapest option. At a later date (inspired by you Cherryrig) I'd like to pick up a few cheap flashes and control them all from the camera, but at the moment I'm after the cheap as chips option.
I should point out for clarity that the flash has a minolta fitting, so won't fit on the D80, so any connection would need to be nikon at one end and minolta at the other