If you are willing to do a little minor work.
Check out Modest Magic .com. This guy lazer cuts high density foam on the cheep! Wall pieces for dungeons and buildings that snap together. slap on a base coat and a dry brush and BAM, table full of terrain. He has more than wall pieces and he does custom stuff too. I haven't ordered anything yet but I plan on it. I will post a review when I do. Definitely check this out if you have worked with foam before and want a cheep, quick way to put a ton of precision terrain on your table.