I'm rehabbing a 1650 square foot house. Roof/replacement windows/gutted kitchen/paint/new water heater. Going to have to do a bathroom under the same roof because it's a 3/1. My brother in law is a builder/investor and he and I sat in the car after the closing and just talked through what the estimates would be. I keep checking that list and he came very close on most items. Including closing costs, etc. I've spent $28,000 and I haven't paid off the painter nor starting getting the cabinets built. Does include the granite order though. That's expensive and depends so much on what you want.
Of the houses we did last year, the remodeling costs ran from $28,000 to $60,000 and all involved new roofs, some new Heating and Air, new kitchens etc. I have no idea what building a bathroom inside the structure will cost but I'll bet it's going to run $10-$15k. A friend of mine just did his first bathroom and his costs ran $10,000 in a small house. When you get through you could easily spend $40K, $50K and really not be sure the house will sell in this market to make a decent profit for your trouble. Better yet, move in it for two years, let it appreciate and then take your tax free gain. I'm prohibited due to 1031 exchange but that's what I'd do if I could.
Get a builder/friend to run that list of wants with you. It'll be invaluable. Time is money when you're rehabbing and I'm hoping to only have made 3 mortgage payments by the end of kichen and the floor sanding next month. And I had 53% equity in the house when I started.