I posted this on a different post but I have used a contractor for many of my flip homes that has altered homes to help me sell them. He could help you figure out prices and the approximate increase in value. He has helped me a lot and thats why I am giving his info out. He has added an extra bathroom in one of my places and it helped things along in a sale.
I have had two homes remodeled (added a bathroom and redid the kitchen in one and the other redid both bathrooms and added an extra dining area and completly remodeled the kitchen and fireplace and the best and lowest bid I found for both jobs was a local contractor. He did great work, but I had to wait to get the second job done because he had a list of clients waiting for him (probably the low prices and the attention to detail, the tiles were all hand finished and it was amazing in the end esp for the price).
He would probably be able to come out and give you an estimate incase you were interested his number was 801-494-4924. Only thing I have noticed is he doesnt check his voice mail messages unless he recognizes the number and so call until you get ahold of him in person, I seriously would recommend him. firstname.lastname@example.org that is his e-mail and his name was James. Id go with him again so Id at least get him to get you an estimate because I have had some terrible work done by others that charged more and Ive never had issues with his work actually having him come in and fix the work a previous contractor did on a house I am flipping. Godd luck. and an extra bathroom always helps, I had him add one too.