Senji Studios did a review of Ziterdes Iron World terrain that they consider a good substitute for Forge World terrain. Does it hold up?
From the review:
Forge World recently released the Zone Mortalis rule set. It was fun to play and is designed for indoor combat. There are many options for those that don’t want to
buy the Forge World tiles. The new Iron World scenery by Ziterdes is modular and can be used to represent the inside of a hive world or integrated with other scenery
for urban complexes, and industrial areas.