For one of your table options grouping floating candle vases together is a pretty option for a non-floral centerpieces. To add the "wow", tint the water in some of the vases a dark purple and some a light purple and float gold candles.
Buy rectangular vases, fake flowers, rocks, ribbon, and candles the width of the rectangle. Glue the flowers to the rocks and fill with water. Float the candle up top. Glue the ribbon around the top of the vase.
One way to cut back on centerpieces. - people often overlook designing table set ups in non-traditional fashions and focusing on tablescapes rather than centerpieces to cut costs. Wish I had this at my wedding!