Here's the mossberg I am looking at for a pure waterfowl gun..It would fit in the budget and use the same choke tubes as my 835 so I could use it for turkey as well if I wanted and just turn the 835 into a slug gun.
http://www.ableammo.com/catalog/product_info.php?cPath=9935_13769_13821&products_id=84725
http://www.ableammo.com/catalog/product_info.php?cPath=9935_13769_13821&products_id=84725