I also agree on ebay. Unfortunately there was no ebay when I was preg, but I actually sell maternity clothes on ebay sometimes now. You might prefer to look up "NWT" which is new with tags, meaning brand new. There are some really good things there.
Check the clearance isles too. I bought a cute top at KMart for $1.50 because it had a small pink "stain" on the arm. When I got home, I took some dish soap to the stain--30 seconds later it was non-existant and I had a perfect maternity shirt (sold it on ebay today, actually, with a decent profit). This works too, if you're good at sewing small tears or rips.
Best of Luck, Kelly