To answer the question before with hard numbers... I have a hall closet I was going to convert. It has a total of 11.5 square feet of floor space and vent vertically to ceiling height. Pricing for the shelf setup I wanted, cedar paneling, and with his set-and-forget hunidification for that size of space (tanks, controller, 8 fans) was $900. The only reason I didn't bite the bullet was concerns for household storage space if we had a kid. We got pregnant not 3 months later.
I was concerned with ripping out the Sheetrock and installing fresh for the cedar to cover. Bob told me I could install the cedar directly over the painted wall and it wouldn't cause an issue. Clean it really good and go. The damn door I wanted to replace the existing hollow core door with was almost half the cost LOL!