Maternity Dress vs Regulae Dresses (Sized Up)

Has anyone purchased regular bodycon dresses but in a size or two up for their usual size and used it as a maternity dress? I'm thinking of going this route, as I cant believe maternity dresses are DOUBLE the price and will only be worn for 9 months. I do like how maternity dresses have more stretch, but I just cant justify spending almost $100 on a few pieces. Old navy, Target and H&M; are exspensive. It gets 90+ degrees here in the summer so I definitely need something to wear but in my budget!