Perhaps a little bit cheaper than the giant centrepieces with lots of branches. With the tree branches idea of getting them and painting them white would really pretty if we hung crystals on them and maybe added some flowers (if we get good ones)
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.
Manahawkin Wedding at the Mallard Island Yacht Club by Kay English Photography
Submerged Calla Lilly Centerpieces: I could also show you a couple of pieces with water pearls that might be a good idea. This is simple and elegant. I LOVE THIS CAN ONE OF YOU DO THIS? with purple calla lilies and white candles