I'm sure it's cheaper than the pre-cut foam.If you go with poret foam you'll have to cut the sheets to fit, easy peasy. Forgot to mention that
Are you saying that I should get 6 L of it?My personal favorite is eheim substrat pro. I have 6 L of it in each of my 2262's. I also like seachem matrix, although it does clog up a little bit easier. You can get 6 L of substrat pro on Amazon for under $80.
http://www.amazon.com/Substrat-Biological-Filter-Sintered-Pearl-Shaped/dp/B0002Z7VAK