While there are standard resolutions for DVD-video, there isn't really a standard bitrate. I believe that a player must be able to sustain a transfer rate of at least 8000kbps to be considered compliant, unless its higher.
You see, you can make choices for both video and audio bitrate when you encode video to mpeg 2, and that could be anything from constant bitrates of (I don't really know what the minimum is) maybe 2000kbps, up to 8000 or higher (if you don't mind making a non standards compliant disc), or you can use a variable bitrate strategy.
The same goes for audio, in terms of format and bitrate (mp2@224,384, linear PCM, god knows what all you can use)
The real question is, "how much can you get on a disc at a quality you find acceptable?" and that is going to vary depending on your video, and what looks acceptable to you.
I've encoded my amv a couple times, one at an extreme 9000kbps cbr, and later at high quality vbr, which came out around 230mb before audio, IIRC.
I also think I recall a vob that contained an entire episode of Lain, with video, two audio tracks, and subs, coming out at around one gigabyte.
That might explain why the DVD encoding on Lain sucks, too low a bitrate.
Maybe someone more familiar with the technical details will correct or expand on some of what I've said...