Once Wisp is fully reformed you are given the two choices for your item reward; "Something New" or "Something Expensive". You can receive flooring, wallpaper, clothing, or a furniture item, but only 1 reward is available each visit. As Wisp alludes to, "Something Expensive" is not always expensive, as it will be an item with a buying price of 10,000 bells or less. "Something New" is an item not in your catalog, and this will be worth 1,500 bells or less. Below are the reward types Wisp could potentially hand out and their chance in %.
If you live in a house... Furniture - 40% Wallpaper / Flooring - 24% Bed - 24% Clothing - 12%
If you live in a tent... Furniture - 75% Wallpaper / Flooring - 0% Bed - 0% Clothing - 25%
Photos taken by GavinGoneGlobal Item percentages from the Official New Horizons Companion Guide