Piggybacking from this post https://www.ozbargain.com.au/node/269312
I think this is the cheapest I've ever seen for a Sennheiser HD600.
I've just tried it, and it showed me $299 delivered (after the GIVEME50 coupon code is applied)
Note having owned these a good 2-3 years in the past, you absolutely need an amp for these to sound any good. IMO they are best for classical, the transient response was too slow for something like metal or EDM and I would recommend others for soundstage (width / height).
Wouldn't really recommend them (I ended up selling mine), but I know quite a few on head-fi used to really like these and the HD650s (which are bassier versions of the HD600s).
The cheapest this has ever been was when ausd was above parity, and you could buy it from amazon uk for 220 ausd. Still a great deal when considering where the dollar is at today.
I think I paid $399 from noisy motel a year ago or so. Can't recommend these headphones enough. Fantastic quality and work great with my FiiO setup.
Seems like a good deal. I got mine for $269 ($288 shipped) from Kogan in 2013, and the dollar was above parity back then.