You can also DIY your own silk plants for much cheaper. You'll need to head to a craft store or walmart and pick up some of their fabric plants. Then you'll need to take some wire cutters and needle-nosed pliers and pull out any metal in the stems/branches. Once you've done that, soak them for a week or so in whatever water conditioner/stuff you use in your tanks to make sure the colors don't bleed and they don't cloud the water.
To get them to stay put in your tank, you take some aquarium silicone and glue some polished rocks (again, avail at craft stores) to the bottoms, and you're good to go. Most of the silk flower/greenery sprays at walmart are a dollar, and you can find some nice stuff there. :) So much cheaper. :)