i’ve found getting bigger sheets of foam and having them laser-cut to the appropriate sizes to be pretty incomparable.
the materials cost almost nothing—i’ve even had a foam store give me the piece i needed for free in the past. the cutting, on the other hand, can be somewhat expensive, but very much worth it in my opinion—you’ll never worry about the fit again.
the place i like best is called foam mart—if you’re ever in the los angeles area i highly recommend them start to finish.