How fast you can write: It is all about the quality of the media and the speed of your computer and recorder.
Since a few years back I generally use DVD-Rs bought from:
30€ per 100 pcs = 3€ per 10 = 30 cent per disc (that is somewhere near 3 SEK per disc).
They’re claimed to be 16x, but I mostly use 4x. This makes most of them work, I have actually not tried using faster speeds – I’m in no hurry.