If quality is not vital as you say then perhaps you may be able to get away with 120bit mp3s ?!
you should just be able to burn as many as you can JAM/PACK onto a cdr (700mb) if your car/mp3 player plays mp3s from disk
just start a multisession disk with NERO and Just keep adding until its almost full remembering to save a couple of mb to close the disk
then play in your mp3 player
note if your mp3 player/car unit is CD-TEXT compatible then make sure it is ticked in nero options ..note here that really long filenames are a problem with nero so try to keep to around 60 characters or so possibly
Im guessing depending on the length of each track you could maby get about a 100 or so tracks on 1 disk maby more ?!
but...if you car player does not support MP3 then you need the nero MP3 plugin as POACHER Suggested to make mp3 into audio disks
then you will be creating a pretty much normal AUDIO cd that will play in virtually any cd player ...the downside of this is you are really limited to just 80 mins of audio tracks (for a 700mb 80min cdr) and there aint much you can do about that
( unless you go for mono tracks/short tracks and i dont think anyone would do that for music )