its ?300 per side iirc... from protec/tas (bust) and used rally parts etc.
to widen the shell/structure for 18" is gonna cost atleast ?2K to get everything nearly right and that a minimum cost idea...
btw novas are old etc and probably wont get a mag feature bar TV which dosent need some stupid mofo car to get into that... even with some gay looking widness setup.
if you want to be different its probably easier to make it a 3 wheeler.