It's a combination of your ability to give, how close you are to the bride/groom, and the venue. Regardless of how close someone was to my wife and I at the time, I wouldn't expect them to give us $200 if they could not afford to do so. I would feel bad if they did.
$200 should be considered a nice gift in just about any situation. As far as the venue, it's a factor but I would not give $200-250 to a couple I hardly know just because they picked a nice venue.