What a great question about your design budget! I think it is so important to talk about how much you should invest in this project right off the bat! A lot of people have never completely furnished a room in one sitting, so they don’t have any experience in estimating the cost, which leads to sticker shock and awkward conversations.
Lucky for you, I have a furniture pricing worksheet that you can download. This will help you get a general idea of the cost of furnishing a room. However, you will note that this does NOT include many accessories, the cost of items like paint or wallpaper, the cost of trade labor, or the design fees.
This also will not help you figure out a budget for a kitchen or bath project. My best advice is completely ignore any budget you ever saw on HGTV. You can go to Houzz and search kitchen and projects in your area, which were done by designers and get some idea. You might also try googling “high-end kitchen/bath remodel cost”.
Yes, there, I said it. High-end.
If you are working with an interior designer you have just “upped your game”. Meaning, you are not looking for an average outcome for your project. You have taken the time to consult with a professional who will give you a superior experience and a superior design. You are not going to be looking at the average cost of a remodeling project because your project will be above average.