15 dollars at Petsmart (at least the one i got).. And just make sure to clean both sides when your changing water. It lets water move through the divider, but it's still good to get both sides cleaned. I just set one up in my tank, because my M. Estherae was picking on my blood parrots. Anyways, for the one I got it was labeled 29- 55 gallons (and my tank's a 29 gallon). You just cut it to the height or weidth of ur tank depending on what you want.
Cool cool thanks for the suggestion. So far I have had no issues. The barbs have been staying all together and leaving everyone alone for now