The economics of foam are interesting. From what I've been told, the Poret-style polyether foam is harder to come by in the US, evidently due to federal government requirements for fire retardants, although you can find it. Angels Plus carries some. I got over my initial price shock and went with Poret from Swiss Tropicals, because I know it is purpose tested, and I've been happy with my purchases.
There are other options, too. You could use polyfill bedding in your sump. I've used that for years, and it works great, is very cheap (especially on sale), but clogs regularly and will need to be replaced. I've actually been testing two inch polyfill between plastic canvas with blackworm cultures growing in them as mattenfilters, but I'm expecting them to permanently clog eventually. They've been going for about six months now on two of my tanks.