I was looking at some fittings the other day as I had idea for some 4" or 6" pvc also. Over $20 for any of the caps in 4" stupid expensive and YES gouging. Injection molding costs haven't gone up, and material shouldn't be up much either. I think I know why my HD and Lowes stock continues to go up. Heck wandered through getting wood yesterday and 2x4 studs are STILL $4 each.... And my MDF sheet I use is now $44 plus tax for a sheet of half inch. $32 this time last year and that was up 10% from 2019. Wood dust and glue. ARGH