Building terrain, especially for Necromunda, is very simple and can be done on the cheap. There are articles about building terrain all over the web and if you make the mistakes, you can always model it into "battle damage" or play off the fact that the underhive is full of decrepit, leaning, beat up buildings.
I'd never use the planetstrike terrain for Necro, just because of the pricing.
As for the WYSIWYG nature of Necro, I feel your pain. I think this rule helped kill Necro more than any other. If they had produced plastic models for the 6 house gangs and the 3 original outlanders, there would have been alot easier time for players to maintain their gangs within the rules. As it was, your models weapon loadouts could change almost every game depending on new skills, attribute bonuses, or swapping to arm new gangers.
I picked Spyrers as my first gang specifically to not have to deal with that nonsense at all, when I eventually started playing Cawdor, it turned out to be the worst descison possible due to their skill sets vs. what the models were armed with. Too this day, I still peruse the Warhammer fantasy lines to see if any of their human milita or military troops could be converted into Cawdors, but with the masks and hoods the orgininal figures wore, it's just to much trouble for a game too few of my friends want to play anymore.