Your other cheaper option is to work out what ppi that foam is. It just looks like reticulated polyether. Maybe get some off cuts from a foam cutting place to compare density. Or take a guess on a small amount. Looking at it id say a 20ppi would be a good start. A mtr square @25mm is about £50, add on a can of white spray and a template and your still a lot better.
Have a Google fir air filtration foam. Germany make the best foams generally, but there are loads if British based companies that at least sell/cut it. They might even let you send it in and tell you what you need.
Edit: In fact you can buy a chunk foe £8 on ebay, sold as 20ppi aquarium foam. Start there and see if you need more or less ppi. 10 is supper soft and smooth if I recall, 45 is quite rough and course so somewhere in between. It goes up in increments so your not quibbling over single didgets. I think 10 , 20, 30, 45, 60, 80 ppi if u recall.
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