Prenatal vitamins?!?

Beth
My dr wrote me a prescription for a prenatal vitamin with dha of my choice.  The only choice at our local pharmacies will be $50+ every month.  Is anyone taking an over-the-counter vitamin?  If so, which one are you taking?  I just can't see spending $400~ on vitamins over the course of my pregnancy when it seems like the OTC vitamins contain the same ingredients!!!!!