What is an easy way to make inexpensive terrian for warhammer 40k?

See what you have around. Cardboard cut out to be a city fight board is probably the quickest and cheapest to make. Cut out the buildings, tape them together, and base them on cardboard. Then get some textured spray paint in black/rock color and spray paint them. I've built lots of terrain for our club this way for about $5 a set including paint and tape. Cardboard is everywhere so that was "free"