I don't think there is a generic walking foot that works on a Bernina. I think the Bernina walking foot costs about $139.00. Try lining up and measuring for the 1 /4" seam, you may not need a separate foot. Use it for a while before deciding if you need a stitch in the ditch foot.
Have you posted these questions in the Vintage and Antique Sewing Machines forum? The old style 830 and 930 are still highly prized.