Little background, I am a DNN newbie. I have worked with Epicor for 10+ years. Including populating the Sales header (orders) and Detail (ord_list) tables with new orders. I would think you would build a layer between the two programs. Use a DNN order module to create the order (you should be able to write some procs to go get price from the part_price table). Take the needed information from the DNN order module and transform it to Epicor's tables. I would stay away from editing the Epicor tables, you are just asking for issues.

Good luck and hopefully this doesn't come too late.

Bryan