Walthers is a good reference as a catalog, in my experience as a Z modeler Walthers is so much expensive.
Marklin is the largest Z scale maker in the world.
AZL is an american Z scale maker, outstanding detail but quiet expensive
etc.
Depends on what you want to model: European or american.
Z Prices are quiet better now and quality and detailing are greater, I can recomend you to view the following pages:
Yeah the marklin's were alot, i went to a train show and saw them he had a electric britsh engine and it was for sale for $300 so when i saw that i was amazed how much it was.