A lot. You will definitely need to talk with a contractor and they will be able to price it out for you. It might make more financial sense to sell your current home and buy a new home to meet your expanding needs.... more
Looks like similar homes are selling between $190k and $220k. If you click on the "web references" link, you'll see a report based on 1mi radius from your home, 3br/2ba, 1000-1400 sq ft, sold in the last three months.
If you want to get more granular or specific with your price opinion request, please let me know Neige.... more