What I've read about the GDR is that money was rarely the problem. You couldn't spend the money if what you wanted to buy was simply not available (except maybe in "Intershops" where you needed to pay in Western currency, that was in fact very expensive). It really was a different system.

Yes the movie Night Crossing also shows very well that there was a lot of suspicion, for example they had to buy the fabric from lots of different places and this a slipup actually caused them to be ratted out (not sure if this particular part of the story happened to these people in real life too but it was really a thing)