Hey I made my own out of 5/4 in by 6 in treated top choice decking boards... it was so easy... total costs running about $125.00 per window, some of my windows are 3X6 too, price includes all shutter hardware, wood, silicone paintable caulking, stainless steel screws, and four coats of paint.. and they won't rot or rust and are a full inch thick... they're of the board and batten design... hardest part is all the painting... piece of cake building them.... oh, and they really look nice too... I should have done this 20 years ago....