Although this video is focused on Warhammer 40K, I think the techniques shown for building terrain entirely out of cardboard are worth studying.
Hills are among the most basic sort of terrain you need for a wargames table. Here’s some nice advice on building inexpensive cardboard hills.
Here’s some good advice on quickly building a relatively inexpensive wargames table.
Ironhands has a page with tips for creating sufficiently alien Eldar terrain for your Warhammer 40K games.