S.C.
You can try Once Upon A Child. It's in Glenbrook Commons beside Toys R Us. They sell gently used maternity clothes. Also Motherhood Materinity in the Glenbrook Mall has some reasonably priced things, especially if you hit them at sale time. Plus their clothes are really durable. I only bought 2 pairs of pants and they lasted me my entire pregnancy. Kohl's is another good place. They always have sales. Try to hit some of the early morning sales, those are always the best prices. I was like you and wasn't at all financially able to afford all the stuff I really wanted :) Don't forget about Wal-Mart and Meijer. I got some really great shirts there for under $10.00 each.
Good luck,
Shaun