I used to think like that, but then I listened to a few Superlux modelsjestermgee wrote:If you were to have an absolute "min" I would set your bar at about $100.
More impressions here: http://www.headfonia.com/superlux-hd668b/
The Superluxes are compatible with AKG-240 velour pads, which I strongly recommend. The overall price is still $50ish if going that route, depending on the model.