Your car player will almost certainly not play dvds. DVDs use a different frequency laser than those used for cds.
And audio books don't lend themselves to compression that can be readily played back. You can compress into something like a rar file, but that gets you nowhere for playing back on a cd player. You can also re-record the whole thing at a lower bitrate and possibly get a smaller output size, but 1.3gb to 700mb? I don't think so.
What you could do is chop the original in two and put it on two cds. This assumes your car player can handle mp3 data files. MP3 files do not equal CD audio.
Or if your player can accept usb flash drives, put the entire thing on one of them.