Maybe try contacting the guy at
filterbag.com and asking if they've made socks for the Red Sea Reefers (if they're different than the Max's socks) and had success with making them. Or maybe you could send him a sock that's almost out of commission so they can make it fit identically, but not clog like that. It's the ring of the sock, I assume, why you can't use other socks?
Because they make filter socks for EVERY type of industry (aquarium, oil and gas, ect...) and every aspect of the sock is customizable from the micron rating, size of the sock, felt or mesh and if you want polypropylene felt or regular, plastic rim at the top, regular or drawstring.
Because even if they have to custom make them, which is what I did, I can almost guarantee they would be much cheaper than $10. The only thing with a custom order is you need to get at least 25 socks minimum, unless, like you said, you find another way around it.
Sorry, couldn't edit my previous post any longer. They have tabs holding the sock in place right? So if you get a sock with a round plastic ring at the top, is it possible to just cut a nook out of the plastic ring instead of modifying the sump?