Is $450 to retrofit a 4-inch filter cabinet with Aprilaire 90 degree rack a fair price?

I've been debating switching to a 4-inch filter cabinet on my mid-efficiency furnace. I like the idea of more airflow with better filtration and changing filters less often. I'm looking for opinions on whether it's worth it. I need a solution that works with my vertical return ducting, which pipes back into the side of the furnace, requiring a hard 90-degree angle. The space available is about 18.5 inches from the right wall to the side of the furnace and 25 inches from the front of the return to the back wall. The factory cutout for the furnace return filter is 23x14 inches, and I'm unsure if I can use a larger filter than 16x25 inches. The furnace manual allows for side returns unless CFM is over 1800; my fan settings are med/lo, with CFM ranging between 1438-1186. My furnace is 100k BTU, but it's de-rated to maybe 80k BTU due to 5k elevation. I have 7 return ducts and 14 registers.