Most of those are really not very dressy and are jersey material. I am assuming that it is at least somewhat of a formal occasion, since you said that most of your dresses you have now are not nice enough. The second one is a bit dressier, though I am not a big fan.
Have you looked at minefornine.com or similar websites? Then you could get something a little fancier for a fraction of what it cost to buy it (since you probably won't have much of a need for a fancy maternity dress again, right).