I guess expensive is relative. So, I guess the better question is what is your budget? I’ve seen some second hand ones for fairly good price on fb marketplace.
Ok so what is your budget and are you opposed to a hang on back filter? That’s what I use for my 40 gallon breeder. You can always diy an overflow cover to hide part of it
I found these but just depends on what you’re looking for. Internal filters are inexpensive but I’m not sure about performance. Maybe you could diy a sump with a 10g tank? I’m sure there are already threads about that if you do a search.